Differential pressure power generation maximum power point tracking control method and device based on dual modes

Abstract

The invention discloses a differential pressure power generation maximum power point tracking control method and device based on dual modes, and belongs to the field of natural gas control. The method comprises the steps that a system model is constructed, maximum power tracking method analysis is conducted, and a variable speed differential pressure power generation system model based on a turbo expander is constructed; and dual-mode differential pressure power generation MPPT control is carried out based on combination of an optimal characteristic ratio method and a variable step size hill-climbing search method. The method can adapt to different environmental conditions, improves the energy utilization efficiency of the differential pressure power generation system, can achieve the efficient and stable operation of the differential pressure power generation system, can give consideration to the tracking accuracy and stability of the two algorithms, and has a good application value.

Description

Technical Field

[0001] The present invention relates to the field of natural gas control, and more specifically, to a dual-mode-based pressure difference power generation maximum power point tracking control method and device. Background Art

[0002] As a clean energy, natural gas has been expanding its share in the energy market in recent years. The International Energy Agency predicts that global natural gas demand will increase by 50% in 2040. From production to use, natural gas needs to go through multiple levels of pressure regulation before it can be finally delivered to the user end. The traditional pressure regulation process mostly uses the form of a pressure regulating valve, which causes a lot of waste of pressure energy. Taking China's West-East Gas Pipeline I system as an example, its annual recoverable pressure energy is close to 2400GWh. Natural gas pressure difference power generation technology can make full use of the pressure energy in the natural gas pipeline network, which is of great significance for vigorously developing clean energy and promoting the transformation of my country's energy structure. The basic principle of natural gas pressure difference power generation is that high-pressure natural gas enters the expander for isentropic expansion and acceleration, and the high-speed airflow drives the generator shaft to rotate through the impeller to generate electricity.

[0003] In the 1960s, Long Qingyan and others developed an expander that used high-pressure gas in the carboniferous gas reservoir to generate electricity, with a power generation capacity of 3.5kW. The United States, Iran, Canada and other countries have also conducted research on natural gas pressure differential power generation, but it has not been widely used. Since the 21st century, due to the tense global energy situation and the need for low-carbon development, natural gas pressure differential power generation technology has been widely studied.

[0004] Due to the large volatility and high uncertainty of natural gas pressure differential power generation, how to efficiently utilize natural gas pressure energy has become a research focus in recent years. Neseli et al. conducted a study on pressure energy power generation for a natural gas pressure regulating station in Izmir and established the energy analysis and design of the heater, heat exchanger, turbine expander and the entire system of the natural gas pressure differential power generation device. Analytical model. Li designed an integrated energy system consisting of an expander subsystem and an organic Rankine cycle subsystem, which are used to recover the pressure energy and cold energy and low-grade thermal energy of natural gas respectively. Zhang Anan constructed a microgrid optimization scheduling model in which a natural gas pressure difference power generation device is used as both a power source and a load. The simulation verified that the combination of the natural gas pressure difference power generation system and the microgrid can improve the utilization rate of natural gas pressure energy and reduce the scheduling cost of the microgrid. Wang Yanliang designed a distribution vehicle and battery replacement scheduling method considering the "centralized charging and unified distribution" operation mode of battery-swap electric vehicle charging stations, effectively improving the natural gas pressure energy consumption rate.

[0005] At present, there are endless studies on the multi-energy utilization and local consumption of natural gas, but the potential for energy utilization of the pressure difference power generation device itself remains to be explored. Ji Guanghua proposed the decisive parameter that determines the thermal performance of the turbine expander - the characteristic ratio, and gave the relationship between the expander characteristic ratio, speed and efficiency. Chen Ning found in the pressure difference power generation project research of Yitangmen Station that the output power of the expander first increased and then decreased with the increase of speed, but no further research was conducted. Hu Jian and others applied the turbine expander to the refrigeration cycle for helium cooling, and improved the efficiency of the turbine expander by controlling the speed, but did not study the recovery of mechanical energy. Under the influence of comprehensive factors such as gas conditions, machine structure, equipment materials, etc., most pressure difference power generation devices have a maximum efficiency point in fluid mechanics. It is of great significance to study how to use automatic control methods within the adjustable range to maximize the efficiency of pressure difference power generation, which is of great significance to improving energy utilization. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a dual-mode pressure difference power generation maximum power point tracking control method and device, which can adapt to different environmental conditions and improve the energy utilization efficiency of the pressure difference power generation system; can realize the efficient and stable operation of the pressure difference power generation system; can take into account the tracking accuracy and stability, can quickly optimize to the optimal working point under different working conditions, and has good application value.

[0007] The object of the present invention is achieved through the following solutions:

[0008] A dual-mode differential pressure power generation maximum power point tracking control method, comprising:

[0009] After building a system model and analyzing the maximum power tracking method, a variable speed differential pressure power generation system model based on a turbine expander is constructed, and then the dual-mode differential pressure power generation MPPT control is carried out based on the combination of the best characteristic ratio method and the variable step length hill climbing search method.

[0010] The dual-mode pressure difference power generation MPPT control comprises sub-steps:

[0011] Mode 1: When the operating conditions of the expander change dramatically, the control uses the optimal characteristic ratio method to track the maximum power point;

[0012] Mode 2: When the expander is running smoothly, the distance between the current characteristic ratio and the theoretical optimal characteristic ratio is used as the disturbance step length, and the variable step length hill climbing search method is used to track the maximum power point of differential pressure power generation, so that the motor speed can quickly reach and stabilize at the optimal speed point n opt .

[0013] Furthermore, the construction of the system model and the analysis of the maximum power tracking method specifically include the following sub-steps:

[0014] Step 1.1), establish the mathematical model of the expander: According to the principle of engineering thermodynamics, the working process of the turbine expander is regarded as an isentropic expansion process, and the mechanical power output on the shaft is: Where: W t is the mechanical power output of the turbine expander; Δh is the enthalpy drop of natural gas inlet and outlet; G is the mass flow rate of the natural gas pipeline; η t is the expander efficiency; κ is the constant entropy index, which is a function of the natural gas operating conditions; R g is the natural gas constant; T 1 is the natural gas inlet temperature; p 1 、p 2 are the natural gas inlet and outlet pressures, respectively;

[0015] Step 1.2), construct the mathematical model of PMSG: In the dq synchronous rotating coordinate system, the mathematical model of the permanent magnet synchronous generator is: Where: u d 、u q ,i d ,i q , L q , L q are the components of stator voltage, stator current and inductance on the dq axis, R is the stator armature resistance, ω e is the electrical angular velocity of the motor, ψ f is the permanent magnet flux; considering the surface mounted PMSG, its electromagnetic torque equation is: Where: T e is the electromagnetic torque, n p is the pole pair number;

[0016] Step 1.3), constructing an electromechanical coupling transmission model: The pressure difference power generation system based on the turbo expander usually uses a gearbox to connect the high-speed turbo expander with the medium- and low-speed generator to achieve the matching of speed and power between different mechanical equipment;

[0017] Expander angular velocity ω t The rotor angular velocity ω of the PMSG g The relationship satisfies ω t =G m ω g ; Considering the mechanical loss of the gearbox, the actual mechanical power output to the generator is: W gear =W t η gear ; Combined with the torque formula of PMSG, the electromechanical coupling kinematic equation of the system is: Where: G m is the gearbox transmission ratio, η gearis the gearbox efficiency, J is the motor moment of inertia, and B is the motor damping coefficient;

[0018] Step 1.4), Maximum Power Tracking Method Analysis: By controlling the speed of the generator, the speed of the expander can be controlled through the shaft and the gearbox, so that the characteristic ratio is at the optimal characteristic ratio, and the MPPT control of the turbine expander pressure difference power generation device is realized.

[0019] Furthermore, the expander efficiency η t is the expander characteristic ratio There is an optimal characteristic ratio Corresponding to the maximum efficiency of the expander At this time, the mechanical efficiency of the expander is the highest, and under certain working conditions, the output mechanical power is the largest; the expander characteristic ratio is the circumferential speed u at the impeller inlet 1 The isentropic ideal speed c of the expander s Ratio: Combining the principles of dynamics, The relationship with the expander speed n is: Where: n is the expander speed; D 1 is the diameter of the expander impeller; under certain expander parameters and operating conditions, It is directly proportional to n, that is: There is an optimal speed n opt The mechanical power output of the expander is maximized.

[0020] Furthermore, the maximum power tracking method includes: an optimal characteristic ratio method, a hill climbing search method and an improved algorithm thereof, wherein: the optimal characteristic ratio method calculates the current optimal speed through the expander parameters and the current natural gas operating conditions, and controls the speed accordingly; the hill climbing search method and the improved algorithm impose disturbances on the speed, determine the power changes before and after the disturbance, and perform repeated searches until the maximum power point is reached.

[0021] Furthermore, under certain operating conditions, that is, the natural gas composition, temperature, pressure, and flow rate remain unchanged, the mechanical power output of the turbine expander is only related to the expander efficiency η t related.

[0022] Furthermore, the construction is based on a variable speed pressure difference power generation system model of a turbine expander, specifically comprising:

[0023] Step 2.1), construct a variable speed pressure difference power generation system, specifically including a turbine expander, a gearbox, a generator, a converter and a filter, wherein: the turbine expander converts pressure energy into mechanical energy through an adiabatic expansion process, and transmits it to the generator through the gearbox; the generator converts mechanical energy into AC power through an electromagnetic induction process, and the AC power is connected to the power grid after power conversion and filtering through the converter and filter, thereby completing the entire power generation-grid connection process; and a dual converter back-to-back topology is adopted, specifically including a machine-side converter, a DC capacitor and a grid-side converter, for realizing simultaneous control of the generator speed and the grid-connected power flow;

[0024] Step 2.2), design the control strategy of the variable speed differential pressure power generation system, specifically including: MPPT algorithm, machine-side converter control and grid-side converter control; wherein: the MPPT control algorithm collects the operating parameters of the motor and the expander, calculates the reference speed through the MPPT controller, and transmits the reference speed to the machine-side converter controller; the machine-side converter control adopts a vector control method based on rotor flux orientation, with the motor speed as the control outer loop, and introduces the stator current inner loop to control the electromagnetic torque; the grid-side converter control adopts a vector control method based on grid voltage orientation; the DC side voltage is used as the control outer loop, and the grid-side current inner loop is introduced to control the flow of active power and reactive power.

[0025] Furthermore, the dual-mode pressure difference power generation MPPT control based on the combination of the optimal characteristic ratio method and the variable step length hill climbing search method specifically includes:

[0026] Step 3.1), measuring the current operating conditions of the turbo expander and the generator;

[0027] Step 3.2), select mode 1 or mode 2 in the MPPT algorithm optimization process according to whether the current working conditions change drastically;

[0028] Step 3.3) is to perform the MPPT algorithm optimization process, which specifically includes:

[0029] Mode 1: Calculate the theoretical optimal speed as the expander target reference speed for the next cycle;

[0030] Mode 2: Calculate the power difference and speed difference of this control cycle, calculate the disturbance step length Δn based on this, select the disturbance direction, and obtain the expander target reference speed of the next cycle;

[0031] Step 3.4), store the motor power, speed and expander working condition of this cycle.

[0032] Furthermore, in mode 2 of the MPPT algorithm optimization process in step 3.3), the perturbation step length Where: S is the set step size parameter, which is a constant value. By changing the value of S, the upper limit of the step size is controlled and the overall convergence speed of the MPPT algorithm is adjusted.

[0033] Furthermore, in mode 2 of the MPPT algorithm optimization process in step 3.3), a sub-step is also included: designing a lower limit for the perturbation step size to improve the optimization capability near the MPP.

[0034] A dual-mode pressure difference power generation maximum power point tracking control device comprises a processor and a memory, wherein a program is stored in the memory, and when the program is loaded by the processor, any of the above methods is executed.

[0035] The beneficial effects of the present invention include:

[0036] The present invention makes full use of the advantages of accurate and easy-to-obtain working condition data of the differential pressure power generation system, and uses its characteristic ratio parameters to realize various MPPT algorithms. Different MPPT control algorithms are used in stable working conditions and drastically changing working conditions to balance the relationship between power generation efficiency and system stability. The optimal characteristic ratio method is used under drastically changing working conditions. Although some tracking accuracy is lost, the stability of the MPPT control method is guaranteed. Under stable working conditions, a variable step size MPPT control algorithm is used for optimization, which improves the optimization speed of the algorithm and weakens its oscillation near the MPP.

[0037] The present invention adopts different MPPT control methods when the working condition is stable and when the working condition changes drastically, so as to adapt to different environmental conditions and improve the energy utilization efficiency of the pressure difference power generation system. Simulink is used to verify the proposed dual-mode MPPT control method, which proves that the method can achieve efficient and stable operation of the pressure difference power generation system.

[0038] The present invention combines the best characteristic ratio method with the variable step length hill climbing method, taking into account the tracking accuracy and stability of the two algorithms. The simulation results show that the control algorithm adopted can quickly find the best working point under different working conditions, verifying the effectiveness of the algorithm and having good application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 This is a schematic diagram of the principle of the natural gas pressure difference power generation technology in an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of characteristic ratio-efficiency curve of the turbo expander in an embodiment of the present invention;

[0042] Figure 3 The structure and principle diagram of the variable speed pressure difference power generation system in the embodiment of the present invention;

[0043] Figure 4 This is a flow chart of the dual-mode pressure difference power generation MPPT algorithm in an embodiment of the present invention;

[0044] Figure 5 This is a simulation diagram of the expander inlet pressure in an embodiment of the present invention;

[0045] Figure 6 It is a simulation diagram of the characteristic ratio of the turbine expander in the embodiment of the present invention;

[0046] Figure 7 This is a simulation diagram of the efficiency of a turbo expander in an embodiment of the present invention;

[0047] Need to explain, Figure 6 and Figure 7 The color distinction is to facilitate understanding of the simulation results of the solution of the present invention and is a necessary identification color. DETAILED DESCRIPTION

[0048] All features disclosed in all embodiments in this specification, or steps in all methods or processes implicitly disclosed, except for mutually exclusive features and / or steps, can be combined and / or expanded or replaced in any manner.

[0049] In the conception of the present invention, a maximum power point tracking control scheme for pressure difference power generation based on dual mode is proposed. After building a system model and analyzing the maximum power tracking method, a variable speed pressure difference power generation system model based on a turbine expander is constructed, and then the dual mode pressure difference power generation MPPT control is carried out based on the combination of the optimal characteristic ratio method and the variable step size hill climbing search method.

[0050] Dual-mode pressure difference power generation MPPT control includes: Mode 1: When the operating conditions of the expander change dramatically, the optimal characteristic ratio method is used to track the maximum power point. The tracking accuracy of the optimal characteristic ratio method is poor, and people in this field generally do not think of it. However, the inventors of the present invention found that the peak and trough of natural gas pressure difference power generation has a relatively obvious regularity. Under the regulation of the expander control system, the proportion of time when the operating conditions change dramatically in a day is not high, so the power loss is relatively small. Therefore, in the conception of the present invention, this method can effectively avoid the problem of misjudgment of direction in the hill climbing method and achieve rapid maximum power point tracking; Mode 2: When the operating conditions of the expander are stable, the distance between the current characteristic ratio and the theoretical optimal characteristic ratio is used as the disturbance step length, and the variable step length hill climbing search method is used to track the maximum power point of pressure difference power generation, so that the motor speed can quickly reach and stabilize at the optimal speed point nopt .

[0051] In a further inventive concept, the maximum power tracking method involved in the scheme of the present invention includes: an optimal characteristic ratio method, a hill climbing search method and improved algorithms thereof. Among them: the best characteristic ratio method calculates the current best speed through the expander parameters and the current natural gas working conditions, and controls the speed accordingly; the principle of this method is simple, easy to implement, with good accuracy and response speed, and the operation of the algorithm only needs to extract operating temperature, pressure, flow and other parameters from the original control system of the expander, without adding additional hardware costs; however, the best characteristic ratio curve is generally obtained from the experimental data of the expander manufacturer, and is easily affected by factors such as equipment aging, and the transplantation effect of the algorithm is not good; the hill climbing search method and its improved algorithm apply disturbances to the speed, judge the power change before and after the disturbance and search repeatedly until the maximum power point is reached; this algorithm has low parameter dependence, good portability, and strong tracking and adaptability; however, its tracking speed is affected by the step size, and due to the existence of disturbances, the motor speed will eventually fluctuate around the optimal speed; another defect of the hill climbing search method is that: within a certain control cycle, if the working conditions change drastically while the generator speed is disturbed, the actual output mechanical power will be affected by both at the same time, which will cause the hill climbing search algorithm to be unable to determine the real cause of the power change, which may lead to misjudgment of the direction.

[0052] In a specific embodiment, Figure 1 As shown, this embodiment relates to a dual-mode pressure difference power generation maximum power point tracking control method, including:

[0053] Step 1) builds a system model and performs maximum power tracking method analysis, including:

[0054] Step 1.1), establish the mathematical model of the expander: According to the principle of engineering thermodynamics, the working process of the turbine expander can be regarded as an isentropic expansion process, and the mechanical power output on the shaft is: Where: W t is the mechanical power output of the turbine expander, kW; Δh is the enthalpy drop of natural gas inlet and outlet, kJ / kg. G is the mass flow rate of natural gas pipeline, kg / s; η t is the expander efficiency; κ is the constant entropy index, which is a function of the natural gas operating conditions; R g is the natural gas constant, which is related to the natural gas composition; T 1 is the natural gas inlet temperature, K; p 1 、p 2 are the natural gas inlet and outlet pressures, MPa, respectively. Under certain operating conditions, that is, the natural gas composition, temperature, pressure, and flow rate remain unchanged, the mechanical power output of the turbine expander is only related to the expander efficiency η trelated.

[0055] Expander efficiency η t is the characteristic ratio Function. Figure 2 As shown, there is an optimal characteristic ratio Corresponding to the maximum efficiency of the expander At this time, the mechanical efficiency of the expander is the highest, and under certain working conditions, the output mechanical power is the largest.

[0056] Expander characteristic ratio is the circumferential speed u at the impeller inlet 1 The isentropic ideal speed c of the expander s Ratio: Combining the principles of dynamics, The relationship with the expander speed n is: Where: n is the expander speed, rpm; D 1 is the diameter of the expander impeller, m; under certain expander parameters and operating conditions, It is directly proportional to n, that is: Combination Figure 2 Analysis shows that there is an optimal speed n opt , at this time the mechanical power output of the expander is the largest.

[0057] Step 1.2) Construct the mathematical model of PMSG: In the dq synchronous rotating coordinate system, the mathematical model of the permanent magnet synchronous generator is: Where: u d 、u q ,i d ,i q , L q , L q are the components of stator voltage, stator current and inductance on the dq axis, R is the stator armature resistance, ω e is the electrical angular velocity of the motor, ψ f is the permanent magnet flux. Considering the surface mounted PMSG, its electromagnetic torque equation is: Where: T e is the electromagnetic torque, n p is the pole pair number.

[0058] Step 1.3), construct an electromechanical coupling transmission model: Under normal operating conditions of differential pressure power generation, the rated speed of the turbo expander is generally in the range of 6000 to 30000 rpm. Since high-speed motors are limited by the complexity and power of the control algorithm, the differential pressure power generation system based on the turbo expander often uses a gearbox to connect the high-speed turbo expander with the medium and low-speed generator to achieve speed and power matching between different mechanical equipment.

[0059] Expander angular velocity ωt The rotor angular velocity ω of the PMSG g The relationship satisfies ω t =G m ω g ; Due to the mechanical loss of the gearbox, the actual mechanical power output to the generator is: W gear =W t η gear ; Combined with the torque formula of PMSG, the electromechanical coupling kinematic equation of the system is: Where: G m is the gearbox transmission ratio, η gear is the gearbox efficiency, J is the motor moment of inertia, and B is the motor damping coefficient.

[0060] Step 1.4), Maximum Power Tracking Method Analysis: By controlling the speed of the generator through any of the following methods, the speed of the expander can be controlled through the shaft and the gearbox, so that the characteristic ratio is at the optimal characteristic ratio, and the MPPT control of the turbine expander pressure difference power generation device is realized.

[0061] The maximum power tracking method includes: the best characteristic ratio method, the hill climbing search method and its improved algorithm, among which: the best characteristic ratio method calculates the current optimal speed through the expander parameters and the current natural gas working conditions, and controls the speed accordingly. The principle of this method is simple, easy to implement, with good accuracy and response speed, and the operation of the algorithm only needs to extract operating temperature, pressure, flow and other parameters from the original control system of the expander, without adding additional hardware costs. However, the best characteristic ratio curve is generally obtained from the experimental data of the expander manufacturer, and is easily affected by factors such as equipment aging, and the transplantation effect of the algorithm is not good. The hill climbing search method and its improved algorithm apply disturbances to the speed, judge the power changes before and after the disturbance, and search repeatedly until the maximum power point is reached. This algorithm has low dependence on parameters, good portability, and strong tracking and adaptability. However, its tracking speed is affected by the step size, and due to the existence of disturbances, the motor speed will eventually fluctuate around the optimal speed. Another drawback of the hill climbing search method is that within a certain control cycle, if the operating conditions change drastically while the generator speed is disturbed, the actual output mechanical power will be affected by both at the same time, which will cause the hill climbing search algorithm to be unable to determine the true cause of the power change, which may lead to a misjudgment of the direction.

[0062] Step 2), construct Figure 3 The variable speed pressure difference power generation system model based on the turbine expander shown in the figure specifically includes:

[0063] Step 2.1), construct a variable speed pressure difference power generation system, including a turbine expander, a gearbox, a generator, a converter and a filter, wherein: the expander converts pressure energy into mechanical energy through an adiabatic expansion process and transmits it to the generator through a gearbox. The generator converts mechanical energy into AC power through an electromagnetic induction process, but due to the inconsistency of frequency, phase, etc., this power cannot be directly connected to the grid. It needs to be connected to the grid after power conversion and filtering through a converter and a filter, thus completing the entire power generation-grid connection process. In order to achieve simultaneous control of the generator speed and grid-connected power flow, this paper adopts a dual converter back-to-back topology, including three parts: a machine-side converter, a DC capacitor and a grid-side converter.

[0064] Step 2.2), the control strategy of the variable speed differential pressure power generation system includes: MPPT algorithm, machine-side converter control and grid-side converter control, wherein: the MPPT control algorithm collects the operating parameters of the motor and the expander, calculates the reference speed through the MPPT controller, and transmits the reference speed to the machine-side converter controller; the machine-side converter control adopts a vector control method based on rotor flux orientation. The motor speed is used as the control outer loop, and the stator current inner loop is introduced to control the electromagnetic torque. The grid-side converter control adopts a vector control method based on grid voltage orientation. The DC side voltage is used as the control outer loop, and the grid-side current inner loop is introduced to control the flow of active power and reactive power.

[0065] Step 3), based on the best characteristic ratio method combined with the variable step length hill climbing search method, Figure 4 The dual-mode pressure difference power generation MPPT control shown specifically includes:

[0066] Step 3.1), measuring the current operating conditions of the turbo expander and the generator;

[0067] Step 3.2), select to enter mode 1 or mode 2 according to whether the current working condition changes drastically;

[0068] Step 3.3), perform the MPPT algorithm optimization process;

[0069] Mode 1: Calculate the theoretical optimal speed as the expander target reference speed for the next cycle;

[0070] Mode 2: Calculate the power difference and speed difference of this control cycle, calculate the disturbance step length Δn based on this, select the disturbance direction, and obtain the expander target reference speed of the next cycle.

[0071] Mode 1 means: when the operating conditions of the expander change dramatically, the optimal characteristic ratio method is used for maximum power point tracking. This method can effectively avoid the problem of direction misjudgment in the hill climbing method and achieve rapid maximum power point tracking. Although the tracking accuracy of the optimal characteristic ratio method is poor, the peak and trough of natural gas pressure difference power generation has a relatively obvious regularity. Under the regulation of the expander control system, the proportion of time when the operating conditions change dramatically in a day is not high, so the power loss is relatively small.

[0072] Mode 2 means: when the expander is running smoothly, the distance between the current characteristic ratio and the theoretical optimal characteristic ratio is used as the disturbance step length, and the variable step length hill climbing search method is used to track the maximum power point of differential pressure power generation, so that the motor speed can quickly reach and stabilize at the optimal speed point n opt .

[0073] Perturbation step length Among them: S is the set step size parameter, which is a constant value. The upper limit of the step size can be controlled by changing the value of S to adjust the overall convergence speed of the MPPT algorithm. In actual control, a lower limit is also designed for the perturbation step size to improve the optimization ability near the MPP.

[0074] Step 3.4), store the motor power, speed and expander working condition of this cycle.

[0075] After specific practical experiments, a simulation model was built in Simulink to verify the effectiveness of the designed system and MPPT control method. According to the analysis of the import and export operating data of a certain city's pressure regulating station, it was found that the natural gas inlet pressure fluctuated greatly, while the outlet pressure remained relatively stable. Therefore, this paper mainly analyzes the performance of the MPPT algorithm under the condition of changing inlet pressure. The simulation model parameters are shown in Table 1.

[0076] Table 1 Simulation parameters of natural gas pressure difference power generation system

[0077]

[0078]

[0079] The intake pressure conditions used are as follows: Figure 5 As shown in the figure, the curve is divided into 5 sections according to different working conditions.

[0080] In order to compare the performance of different algorithms, the best characteristic ratio method, variable step size hill climbing algorithm and dual mode method are simulated and compared. Figure 6 and Figure 7 .

[0081] like Figure 6 , Figure 7 As shown in Figure 2, when the system adopts the optimal characteristic ratio method, the expander speed can reach n at the fastest speed.opt Nearby, that is arrive Nearby, and can maintain good tracking effect under various working conditions, but due to the existence of errors, Always with There is a certain gap, and its efficiency is 80.5%, which can never reach (See Figure 7 Zoom1). When the variable step size hill climbing search method is used, the system starts with a larger step size, and its step size decays to a very small value near the MPP. The system oscillates weakly near the MPP. When the working condition is stable (segment1, 3, 5), Can be stable Near the MPP, the maximum expander efficiency of 82% is achieved. However, when the operating conditions change (segment 2, 4), the MPPT algorithm cannot track the MPP in real time due to direction misjudgment, resulting in obvious fluctuations in the characteristic ratio. This phenomenon is consistent with the analysis in Section 2. This poses a great threat to the stability of the entire system. When the dual-mode method is used, the system first starts in mode 2 and quickly tracks to near the MPP, operating at a maximum efficiency of 82%. Subsequently, the operating conditions change, and the algorithm switches to mode 1 at 1.5s, maintaining stable operation of the system at an efficiency of 80.5%. At 2.5s, the operating conditions stabilize again, the system switches back to mode 2, and quickly tracks the actual optimal characteristic point again. The subsequent segments 4 and 5 further verify the effectiveness of the algorithm.

[0082] Compared with the prior art, the method of the present invention adopts different MPPT algorithms under different working conditions, which can effectively avoid the problem of misjudgment of the direction of the hill climbing method when the working conditions change drastically; the difference between the current characteristic ratio and the theoretical optimal characteristic ratio is introduced as the step factor in the variable step size hill climbing algorithm, and the step size is dynamically adjusted according to the measured operating conditions, the current speed and the relationship between the theoretical optimal speed. The simulation results verify that the proposed algorithm can achieve MPPT operation well under both stable working conditions and drastically changing working conditions, effectively improving the energy utilization rate of the pressure difference power generation system.

[0083] It should be noted that within the scope of protection defined in the claims of the present invention, the following embodiments can be combined and / or expanded or replaced in any logical way from the above specific implementation methods, such as disclosed technical principles, disclosed technical features or implicitly disclosed technical features.

[0084] Example 1

[0085] A dual-mode differential pressure power generation maximum power point tracking control method, comprising:

[0086] After building a system model and analyzing the maximum power tracking method, a variable speed differential pressure power generation system model based on a turbine expander is constructed, and then the dual-mode differential pressure power generation MPPT control is carried out based on the combination of the best characteristic ratio method and the variable step length hill climbing search method.

[0087] The dual-mode pressure difference power generation MPPT control comprises sub-steps:

[0088] Mode 1: When the operating conditions of the expander change dramatically, the control uses the optimal characteristic ratio method to track the maximum power point;

[0089] Mode 2: When the expander is running smoothly, the distance between the current characteristic ratio and the theoretical optimal characteristic ratio is used as the disturbance step length, and the variable step length hill climbing search method is used to track the maximum power point of differential pressure power generation, so that the motor speed can quickly reach and stabilize at the optimal speed point n opt .

[0090] Example 2

[0091] Based on Example 1, it is characterized in that the step of constructing a system model and performing a maximum power tracking method analysis specifically includes the following sub-steps:

[0092] Step 1.1), establish the mathematical model of the expander: According to the principle of engineering thermodynamics, the working process of the turbine expander is regarded as an isentropic expansion process, and the mechanical power output on the shaft is: Where: W t is the mechanical power output of the turbine expander; Δh is the enthalpy drop of natural gas inlet and outlet; G is the mass flow rate of the natural gas pipeline; η t is the expander efficiency; κ is the constant entropy index, which is a function of the natural gas operating conditions; R g is the natural gas constant; T 1 is the natural gas inlet temperature; p 1 、p 2 are the natural gas inlet and outlet pressures, respectively;

[0093] Step 1.2), construct the mathematical model of PMSG: In the dq synchronous rotating coordinate system, the mathematical model of the permanent magnet synchronous generator is: Where: u d 、u q ,i d ,i q , L q , L q are the components of stator voltage, stator current and inductance on the dq axis, R is the stator armature resistance, ω e is the electrical angular velocity of the motor, ψ f is the permanent magnet flux; considering the surface mounted PMSG, its electromagnetic torque equation is: Where: Te is the electromagnetic torque, n p is the pole pair number;

[0094] Step 1.3), constructing an electromechanical coupling transmission model: The pressure difference power generation system based on the turbo expander usually uses a gearbox to connect the high-speed turbo expander with the medium- and low-speed generator to achieve the matching of speed and power between different mechanical equipment;

[0095] Expander angular velocity ω t The rotor angular velocity ω of the PMSG g The relationship satisfies ω t =G m ω g ; Considering the mechanical loss of the gearbox, the actual mechanical power output to the generator is: W gear =W t η gear ; Combined with the torque formula of PMSG, the electromechanical coupling kinematic equation of the system is: Where: G m is the gearbox transmission ratio, η gear is the gearbox efficiency, J is the motor moment of inertia, and B is the motor damping coefficient;

[0096] Step 1.4), Maximum Power Tracking Method Analysis: By controlling the speed of the generator, the speed of the expander can be controlled through the shaft and the gearbox, so that the characteristic ratio is at the optimal characteristic ratio, and the MPPT control of the turbine expander pressure difference power generation device is realized.

[0097] Example 3

[0098] Based on Example 2, the expander efficiency η t is the expander characteristic ratio There is an optimal characteristic ratio Corresponding to the maximum efficiency of the expander At this time, the mechanical efficiency of the expander is the highest, and under certain working conditions, the output mechanical power is the largest; the expander characteristic ratio is the circumferential speed u at the impeller inlet 1 The isentropic ideal speed c of the expander s Ratio: Combining the principles of dynamics, The relationship with the expander speed n is: Where: n is the expander speed; D 1 is the diameter of the expander impeller; under certain expander parameters and operating conditions, It is directly proportional to n, that is: There is an optimal speed n opt The mechanical power output of the expander is maximized.

[0099] Example 4

[0100] Based on Example 2, the maximum power tracking method includes: an optimal characteristic ratio method, a hill climbing search method and an improved algorithm thereof, wherein: the optimal characteristic ratio method calculates the current optimal speed through the expander parameters and the current natural gas operating conditions, and controls the speed accordingly; the hill climbing search method and the improved algorithm impose disturbances on the speed, determine the power changes before and after the disturbance, and perform repeated searches until the maximum power point is reached.

[0101] Example 5

[0102] On the basis of Example 2, under certain operating conditions, that is, the natural gas composition, temperature, pressure, and flow rate remain unchanged, the mechanical power output of the turbine expander is only related to the expander efficiency η t related.

[0103] Example 6

[0104] On the basis of Example 1, the variable speed pressure difference power generation system model based on the turbine expander is constructed, specifically including:

[0105] Step 2.1), construct a variable speed pressure difference power generation system, specifically including a turbine expander, a gearbox, a generator, a converter and a filter, wherein: the turbine expander converts pressure energy into mechanical energy through an adiabatic expansion process, and transmits it to the generator through the gearbox; the generator converts mechanical energy into AC power through an electromagnetic induction process, and the AC power is connected to the power grid after power conversion and filtering through the converter and filter, thereby completing the entire power generation-grid connection process; and a dual converter back-to-back topology is adopted, specifically including a machine-side converter, a DC capacitor and a grid-side converter, for realizing simultaneous control of the generator speed and the grid-connected power flow;

[0106] Step 2.2), design the control strategy of the variable speed differential pressure power generation system, specifically including: MPPT algorithm, machine-side converter control and grid-side converter control; wherein: the MPPT control algorithm collects the operating parameters of the motor and the expander, calculates the reference speed through the MPPT controller, and transmits the reference speed to the machine-side converter controller; the machine-side converter control adopts a vector control method based on rotor flux orientation, with the motor speed as the control outer loop, and introduces the stator current inner loop to control the electromagnetic torque; the grid-side converter control adopts a vector control method based on grid voltage orientation; the DC side voltage is used as the control outer loop, and the grid-side current inner loop is introduced to control the flow of active power and reactive power.

[0107] Example 7

[0108] On the basis of Example 1, the dual-mode pressure difference power generation MPPT control based on the combination of the optimal characteristic ratio method and the variable step length hill climbing search method specifically includes:

[0109] Step 3.1), measuring the current operating conditions of the turbo expander and the generator;

[0110] Step 3.2), select mode 1 or mode 2 in the MPPT algorithm optimization process according to whether the current working conditions change drastically;

[0111] Step 3.3) is to perform the MPPT algorithm optimization process, which specifically includes:

[0112] Mode 1: Calculate the theoretical optimal speed as the expander target reference speed for the next cycle;

[0113] Mode 2: Calculate the power difference and speed difference of this control cycle, calculate the disturbance step length Δn based on this, select the disturbance direction, and obtain the expander target reference speed of the next cycle;

[0114] Step 3.4), store the motor power, speed and expander working condition of this cycle.

[0115] Example 8

[0116] Based on Example 7, in Mode 2 of the MPPT algorithm optimization process in step 3.3), the disturbance step length Where: S is the set step size parameter, which is a constant value. By changing the value of S, the upper limit of the step size is controlled and the overall convergence speed of the MPPT algorithm is adjusted.

[0117] Example 9

[0118] On the basis of Example 8, in mode 2 of the MPPT algorithm optimization process in step 3.3), a sub-step is also included: designing a lower limit for the disturbance step size to improve the optimization capability near the MPP.

[0119] Example 10

[0120] A dual-mode pressure difference power generation maximum power point tracking control device includes a processor and a memory, wherein a program is stored in the memory, and when the program is loaded by the processor, the method described in any one of Embodiments 1 to 9 is executed.

[0121] The units involved in the embodiments of the present invention may be implemented by software or hardware, and the units described may also be arranged in a processor. The names of these units do not, in some cases, limit the units themselves.

[0122] According to one aspect of an embodiment of the present invention, a computer program product or a computer program is provided, the computer program product or the computer program includes a computer instruction, and the computer instruction is stored in a computer-readable storage medium. A processor of a computer device reads the computer instruction from the computer-readable storage medium, and the processor executes the computer instruction, so that the computer device executes the method provided in the above various optional implementations.

[0123] As another aspect, an embodiment of the present invention further provides a computer-readable medium, which may be included in the electronic device described in the above embodiment; or may exist independently without being assembled into the electronic device. The above computer-readable medium carries one or more programs, and when the above one or more programs are executed by an electronic device, the electronic device implements the method described in the above embodiment.

[0124] In addition to the above examples, those skilled in the art may obtain other embodiments based on the above disclosure or by using the knowledge or technology in the relevant field to make changes. The features of each embodiment may be interchangeable or replaced. The changes and modifications made by those skilled in the art do not depart from the spirit and scope of the present invention and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A dual-mode differential pressure power generation maximum power point tracking control method, It is characterized in that include: After building a system model and analyzing the maximum power tracking method, a variable speed differential pressure power generation system model based on a turbine expander is constructed, and then the dual-mode differential pressure power generation MPPT control is carried out based on the combination of the best characteristic ratio method and the variable step length hill climbing search method. The dual-mode pressure difference power generation MPPT control comprises sub-steps: Mode 1: When the operating conditions of the expander change dramatically, the control uses the optimal characteristic ratio method to track the maximum power point; Mode 2: When the expander is running smoothly, the distance between the current characteristic ratio and the theoretical optimal characteristic ratio is used as the disturbance step length, and the variable step length hill climbing search method is used to track the maximum power point of differential pressure power generation, so that the motor speed can quickly reach and stabilize at the optimal speed point n opt .

2. According to claim 1, the maximum power point tracking control method based on the dual-mode differential pressure power generation, It is characterized in that The system model is constructed and the maximum power tracking method is analyzed, specifically including the following sub-steps: Step 1.1), establish the mathematical model of the expander: According to the principle of engineering thermodynamics, the working process of the turbine expander is regarded as an isentropic expansion process, and the mechanical power output on the shaft is: Where: W t is the mechanical power output of the turbine expander; Δh is the enthalpy drop of natural gas inlet and outlet; G is the mass flow rate of the natural gas pipeline; η t is the expander efficiency; κ is the constant entropy index, which is a function of the natural gas operating conditions; R g is the natural gas constant; T 1 is the natural gas inlet temperature; p 1 、p 2 are the natural gas inlet and outlet pressures, respectively; Step 1.2), construct the mathematical model of PMSG: In the dq synchronous rotating coordinate system, the mathematical model of the permanent magnet synchronous generator is: Where: u d 、u q ,i d ,i q , L q , L q are the components of stator voltage, stator current and inductance on the dq axis, R is the stator armature resistance, ω e is the electrical angular velocity of the motor, ψ f is the permanent magnet flux; considering the surface mounted PMSG, its electromagnetic torque equation is: Where: T e is the electromagnetic torque, n p is the pole pair number; Step 1.3), constructing an electromechanical coupling transmission model: The pressure difference power generation system based on the turbo expander usually uses a gearbox to connect the high-speed turbo expander with the medium- and low-speed generator to achieve the matching of speed and power between different mechanical equipment; Expander angular velocity ω t The rotor angular velocity ω of the PMSG g The relationship satisfies ω t =G m ω g ; Considering the mechanical loss of the gearbox, the actual mechanical power output to the generator is: W gear =W t η gear ; Combined with the torque formula of PMSG, the electromechanical coupling kinematic equation of the system is: Where: G m is the gearbox transmission ratio, η gear is the gearbox efficiency, J is the motor moment of inertia, and B is the motor damping coefficient; Step 1.4), Maximum Power Tracking Method Analysis: By controlling the speed of the generator, the speed of the expander can be controlled through the shaft and the gearbox, so that the characteristic ratio is at the optimal characteristic ratio, and the MPPT control of the turbine expander pressure difference power generation device is realized.

3. According to claim 2, the dual-mode differential pressure power generation maximum power point tracking control method, It is characterized in that The expander efficiency η t is the expander characteristic ratio There is an optimal characteristic ratio Corresponding to the maximum efficiency of the expander At this time, the mechanical efficiency of the expander is the highest, and under certain working conditions, the output mechanical power is the largest; the expander characteristic ratio is the circumferential speed u at the impeller inlet 1 The isentropic ideal speed c of the expander s Ratio: Combining the principles of dynamics, The relationship with the expander speed n is: Where: n is the expander speed; D 1 is the diameter of the expander impeller; under certain expander parameters and operating conditions, It is directly proportional to n, that is: There is an optimal speed n opt The mechanical power output of the expander is maximized.

4. According to claim 2, the dual-mode differential pressure power generation maximum power point tracking control method, It is characterized in that The maximum power tracking method includes: an optimal characteristic ratio method, a hill climbing search method and an improved algorithm thereof, wherein: the optimal characteristic ratio method calculates the current optimal speed through the expander parameters and the current natural gas operating conditions, and controls the speed accordingly; the hill climbing search method and the improved algorithm impose disturbances on the speed, determine the power changes before and after the disturbance, and perform repeated searches until the maximum power point is reached.

5. According to claim 2, the dual-mode differential pressure power generation maximum power point tracking control method, It is characterized in that Under certain operating conditions, that is, the natural gas composition, temperature, pressure, and flow rate remain unchanged, the mechanical power output of the turbine expander is only related to the expander efficiency η t related.

6. The maximum power point tracking control method based on dual-mode differential pressure power generation according to claim 1, It is characterized in that The structure is based on a variable speed pressure difference power generation system model of a turbine expander, specifically comprising: Step 2.1), construct a variable speed pressure difference power generation system, specifically including a turbine expander, a gearbox, a generator, a converter and a filter, wherein: the turbine expander converts pressure energy into mechanical energy through an adiabatic expansion process, and transmits it to the generator through the gearbox; the generator converts mechanical energy into AC power through an electromagnetic induction process, and the AC power is connected to the power grid after power conversion and filtering through the converter and filter, thereby completing the entire power generation-grid connection process; and a dual converter back-to-back topology is adopted, specifically including a machine-side converter, a DC capacitor and a grid-side converter, for realizing simultaneous control of the generator speed and the grid-connected power flow; Step 2.2), design the control strategy of the variable speed differential pressure power generation system, specifically including: MPPT algorithm, machine-side converter control and grid-side converter control; wherein: the MPPT control algorithm collects the operating parameters of the motor and the expander, calculates the reference speed through the MPPT controller, and transmits the reference speed to the machine-side converter controller; the machine-side converter control adopts a vector control method based on rotor flux orientation, with the motor speed as the control outer loop, and introduces the stator current inner loop to control the electromagnetic torque; the grid-side converter control adopts a vector control method based on grid voltage orientation; the DC side voltage is used as the control outer loop, and the grid-side current inner loop is introduced to control the flow of active power and reactive power.

7. The maximum power point tracking control method based on dual-mode differential pressure power generation according to claim 1, It is characterized in that The dual-mode pressure difference power generation MPPT control based on the combination of the optimal characteristic ratio method and the variable step length hill climbing search method specifically includes: Step 3.1), measuring the current operating conditions of the turbo expander and the generator; Step 3.2), select mode 1 or mode 2 in the MPPT algorithm optimization process according to whether the current working conditions change drastically; Step 3.3) is to perform the MPPT algorithm optimization process, which specifically includes: Mode 1: Calculate the theoretical optimal speed as the expander target reference speed for the next cycle; Mode 2: Calculate the power difference and speed difference of this control cycle, calculate the disturbance step length Δn based on this, select the disturbance direction, and obtain the expander target reference speed of the next cycle; Step 3.4), store the motor power, speed and expander working condition of this cycle.

8. The dual-mode differential pressure power generation maximum power point tracking control method according to claim 7, It is characterized in that In step 3.3) of the MPPT algorithm optimization process, in mode 2, the perturbation step length is Where: S is the set step size parameter, which is a constant value. By changing the value of S, the upper limit of the step size is controlled and the overall convergence speed of the MPPT algorithm is adjusted.

9. The dual-mode differential pressure power generation maximum power point tracking control method according to claim 8, It is characterized in that In mode 2 of the MPPT algorithm optimization process in step 3.3), a sub-step is also included: designing a lower limit for the perturbation step size to improve the optimization capability near the MPP.

10. A dual-mode pressure difference power generation maximum power point tracking control device, It is characterized in that The invention comprises a processor and a memory, wherein a program is stored in the memory, and when the program is loaded by the processor, the method according to any one of claims 1 to 9 is executed.

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