Control method of high-speed dual three-phase permanent magnet synchronous generator

Abstract

The invention discloses a control method of a high-speed dual three-phase permanent magnet synchronous generator, which comprises the following steps of: constructing a mathematical model of the high-speed dual three-phase permanent magnet synchronous generator by utilizing equal-amplitude vector space decoupling and synchronous rotation coordinate transformation, and obtaining a gas-machine-electricity coupling mathematical equation in combination with an output mechanical power expression of a rotating shaft of an expansion machine; constructing a back-to-back dual PWM converter vector control method, and controlling the rotating speed and the current harmonic wave of the synchronous generator; a current loop and electric energy quality of the synchronous generator are optimized through a fundamental current loop based on an active resistor and a harmonic current loop based on a quasi-proportional resonance regulator; and controlling the output power of the synchronous generator by using a dual-mode differential pressure power generation MPPT control strategy to obtain a final control method. The invention relates to the technical field of gas differential pressure power generation, and solves the technical problems of poor motor control precision, poor electric energy quality, weak adaptability under complex working conditions and the like in a traditional gas differential pressure power generation system.

Description

Technical Field

[0001] The invention belongs to the field of gas pressure difference power generation, relates to a control technology of a high-speed dual three-phase permanent magnet synchronous generator, and specifically is a control method of a high-speed dual three-phase permanent magnet synchronous generator. Background Art

[0002] In the field of energy utilization and conversion, gas pressure difference power generation, as an important technical means, aims to convert the energy contained in the gas pressure difference into electrical energy. It plays a key role in many scenarios such as industrial waste pressure recovery and natural gas transportation, and is of great significance for improving energy utilization and reducing energy consumption.

[0003] Traditional gas pressure difference power generation systems usually consist of expanders, generators, and supporting control devices. In terms of power generation efficiency, the energy potential of gas has not been fully tapped due to insufficient coordinated optimization between the various components of the system. For example, the operating conditions of the expander and the working characteristics of the generator have not been accurately matched, resulting in some energy being wasted during the conversion process, and the overall power generation efficiency is difficult to reach the ideal level. In terms of motor control accuracy, traditional systems mostly use relatively simple control strategies, which are difficult to cope with the multi-variable strong coupling characteristics of high-speed dual-three-phase permanent magnet synchronous generators under complex working conditions. The motor model in the natural coordinate system is complex, resulting in poor speed and current control accuracy, affecting the stable operation and power generation performance of the motor. In terms of power quality, harmonic problems are prominent. The harmonic currents generated when the generator is running are not effectively suppressed. These harmonics will not only increase the loss of the motor itself, but may also interfere with the normal operation of the power grid, reduce the power quality, and have adverse effects on other electrical equipment in the power grid. Faced with complex and changeable working conditions, such as large fluctuations in gas flow, pressure, and temperature, traditional systems lack effective response mechanisms. Especially during peak and trough periods of residential gas consumption, significant changes in gas conditions make it difficult for the power generation system to adapt quickly and cannot always maintain an efficient and stable operating state, which seriously limits the widespread application and further development of gas pressure difference power generation technology. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art; to this end, the present invention proposes a control method for a high-speed dual three-phase permanent magnet synchronous generator, which is used to solve the technical problems existing in traditional gas pressure difference power generation systems, such as poor motor control accuracy, poor power quality and weak adaptability under complex working conditions.

[0005] To achieve the above object, a first aspect of the present invention provides a control method for a high-speed dual three-phase permanent magnet synchronous generator, comprising:

[0006] S1, using equal amplitude vector space decoupling and synchronous rotating coordinate transformation, the mathematical model of high-speed dual three-phase permanent magnet synchronous generator is constructed, and the gas-machine-electric coupling mathematical equation is obtained in combination with the output mechanical power expression of the expander shaft;

[0007] S2, a back-to-back dual PWM converter vector control method constructed based on the gas-machine-electric coupling mathematical equations to control the speed and current harmonics of the high-speed dual three-phase permanent magnet synchronous generator;

[0008] S3, optimizes the current loop and power quality of the high-speed dual three-phase permanent magnet synchronous generator by designing a fundamental current loop based on active resistance and a harmonic current loop based on quasi-proportional resonant regulator;

[0009] S4, using the dual-mode pressure difference power generation MPPT control strategy to control the output power of the high-speed dual three-phase permanent magnet synchronous generator, and obtaining a control method for the high-speed dual three-phase permanent magnet synchronous generator.

[0010] In order to ensure the operating energy efficiency and power-to-volume ratio of the gas pressure difference power generation device at the same time, the present invention uses a high-speed dual three-phase permanent magnet synchronous generator for direct drive and grid connection. By establishing a gas-machine-electric integrated model based on a gas expander, a back-to-back dual PWM converter vector control system is constructed. And for the high-speed working condition of the motor, a current loop is designed, and a maximum power point tracking (maximum power point tracking, MPPT) control algorithm for pressure difference power generation suitable for complex gas working conditions is explored. At the same time, in order to achieve a fast and accurate response to current changes and suppress other disturbances, the present invention redesigns the current loop of the high-speed motor based on the fundamental current loop of the active resistor and the quasi-proportional resonant regulator. Finally, based on the dual-mode pressure difference power generation MPPT control strategy, the power generation process under different working conditions is optimized and controlled to balance the efficiency and stability of the system operation.

[0011] Furthermore, the mathematical model of the high-speed dual three-phase permanent magnet synchronous generator is: T e =3p[(L d -L q )i d +ψ f ]i q , Among them, u d 、u q 、u x 、u y They represent the dq and xy components of the stator voltage respectively, i d 、i q 、i x 、i y Respectively represent the dq and xy components of the stator current, Rs Indicates stator resistance, L d , L q , L z Represent dq inductance and self-leakage inductance respectively, w e represents the rotor electrical angular velocity, Ψ f represents the permanent magnet flux, p represents the number of rotor pole pairs, J represents the moment of inertia, B represents the damping coefficient, T e Represents electromagnetic torque, T m Represents mechanical torque.

[0012] The mathematical model constructed through equal-amplitude vector space decoupling and synchronous rotating coordinate transformation can accurately describe the electrical characteristics of the generator under complex working conditions, effectively transform the nonlinear high-dimensional model with strong multi-variable coupling, provide a precise theoretical basis for the subsequent control strategy formulation, and help to deeply analyze the operating principles of the motor and achieve precise control.

[0013] Furthermore, the output mechanical power expression of the expander shaft is: Among them, W t represents the output power of the expander in kW, Δh represents the gas enthalpy drop in kJ / kg, Q represents the gas pipeline mass flow in kg / s, η t represents the efficiency of the expander, κ represents the constant entropy index of natural gas, and C p It represents the specific heat capacity at constant pressure, which represents the heat required for the system to increase 1K during constant pressure, C v is the specific constant volume heat capacity, which represents the heat required for the system to increase 1K during the constant volume process. g It represents the gas constant in kJ / (kg·K), T1 represents the inlet temperature in K, P1 represents the inlet pressure, and P2 represents the outlet pressure in MPa.

[0014] Furthermore, the gas-mechanical-electrical coupling mathematical equation is: Among them, w t represents the mechanical angular velocity of the expander working shaft, and w t =w e / p, t indicates time.

[0015] The equation derived from the expression of the mechanical power output of the expander shaft is combined to establish a close connection between the gas expander and the generator, taking into account the synergistic relationship between the two in the energy conversion process, providing a key mathematical basis for the comprehensive control of the entire power generation system, and realizing the optimization of the overall performance of the system.

[0016] Furthermore, the back-to-back dual PWM converter vector control method comprises:

[0017] The motor-side converter uses rotor flux orientation to perform high-performance speed tracking on the coaxially connected high-speed dual three-phase permanent magnet synchronous generator: the high-speed dual three-phase permanent magnet synchronous generator vector control based on VSD coordinate transformation is adopted. The outer loop tracks the generator speed through PI, and the inner loop is a four-dimensional current loop with independent decoupling of the fundamental subspace and harmonic subspace. Four regulators are used to perform closed-loop control on the fundamental current and harmonic current respectively.

[0018] The grid-side converter is oriented with the grid voltage so that the gas pressure difference power generation system outputs electric energy to the grid at a unity power factor: fixed base frequency control is implemented with the bus voltage as the target, and a double closed-loop vector control structure composed of a voltage outer loop and a current inner loop cascade is used to perform command tracking using a PI controller; wherein, the gas pressure difference power generation system includes: an expander, a high-speed dual three-phase permanent magnet synchronous generator, a back-to-back dual PWM converter, a capacitor, a filter and a grid.

[0019] In the back-to-back dual PWM converter vector control method, the motor side uses rotor flux orientation to perform high-performance speed tracking on the generator. The control structure based on VSD coordinate transformation and four-dimensional current loop is adopted, which can effectively decouple the fundamental subspace and harmonic subspace, accurately control the current, improve the speed control accuracy, ensure the stable operation of the generator, and adapt to the requirements of high-speed working conditions; the grid side uses grid voltage orientation to achieve unity power factor operation, and through dual closed-loop vector control and PI controller instruction tracking, it ensures high-quality electric energy integration into the grid, reduces reactive power transmission, and improves grid stability and electric energy utilization efficiency.

[0020] Furthermore, the feedback gain coefficient K of the fundamental current loop based on active resistance is ar , indicating the active resistance setting value.

[0021] Furthermore, the control structure of the harmonic current loop includes using two resonator cascades to track and control the fifth harmonic current and the seventh harmonic current in the harmonic subspace.

[0022] In the fundamental current loop, the setting of the feedback gain coefficient Kar provides a flexible adjustment method for the active resistor. It improves the parameter robustness of the current loop to address the problem of strong current coupling under high-speed conditions, enhances the command tracking and disturbance suppression capabilities, effectively stabilizes the fundamental current, and ensures reliable operation of the motor. In the harmonic current loop, two resonators are cascaded to track and control the fifth and seventh harmonic currents, which can accurately suppress harmonics. Compared with traditional control methods, it significantly improves the power quality and reduces the adverse effects of harmonics on motors and power grids.

[0023] Furthermore, the dual-mode pressure difference power generation MPPT control strategy includes:

[0024] During the peak period of gas consumption for residents, the optimal reference speed of the generator is calculated using the theoretical characteristic ratio, and the MPPT is controlled according to the optimal reference speed;

[0025] During the off-peak period of residential gas consumption, the MPPT is controlled by using a variable step-size hill climbing search method based on the optimal characteristic ratio.

[0026] Furthermore, the theoretical characteristic ratio is: in, represents the theoretical characteristic ratio, u1 represents the circumferential speed at the inlet of the expander impeller, c s represents the isentropic ideal speed of the expander, and c s 2 =2Δh,n t It indicates the operating speed of the expander in rpm; D1 indicates the diameter of the working impeller in m.

[0027] Furthermore, the variable step length hill climbing search method based on the optimal characteristic ratio is: according to the formula Get the step length △n; where s represents the step length factor, Indicates the best characteristic ratio.

[0028] In the dual-mode differential pressure power generation MPPT control strategy, when the residential gas consumption peak period, that is, the gas conditions change dramatically, the theoretical characteristic ratio is used to calculate the optimal reference speed to control the MPPT, which avoids the misjudgment of the search algorithm under complex conditions, and can quickly respond to changes in gas conditions to ensure stable power generation of the system, reduce power fluctuations, and maintain efficient operation of the system under complex conditions of peak gas consumption; when the residential gas consumption is in the trough period, that is, the gas conditions change steadily, the variable step size hill climbing search method based on the optimal characteristic ratio is used to control the MPPT, and the step size is dynamically adjusted according to the distance between the system and the maximum power point, so as to achieve high-precision tracking under stable conditions, fully tap the power generation potential, improve power generation efficiency, and effectively utilize gas pressure energy.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention uses a high-speed dual three-phase permanent magnet synchronous generator to implement direct drive grid connection, eliminating the reduction mechanism, reducing energy loss and device volume, and improving the power-to-volume ratio. At the same time, a gas-machine-electric integrated model based on a gas expander is established, and a back-to-back dual PWM converter vector control system is constructed, which lays the foundation for the stable operation and efficient control of the entire power generation system, and effectively solves the current coupling and instability problems of high-speed dual three-phase permanent magnet synchronous generators;

[0031] In view of the current problem of the motor under high-speed working conditions, the present invention redesigns the current loop of the high-speed motor based on the fundamental current loop of the active resistor and the quasi-proportional resonant regulator, effectively improving the ability of the current loop to cope with the problem of strong current coupling under high-speed working conditions, enhancing parameter robustness, improving current stability, making the motor operation more stable and reliable, and reducing the energy loss and equipment failure risk caused by current fluctuations;

[0032] The present invention adopts a dual-mode pressure difference power generation MPPT control strategy based on the hill climbing search method, which can flexibly switch the control mode according to the changes in the working conditions under complex gas working conditions. Under severe working conditions, the optimal characteristic ratio method is used to quickly realize MPPT control to ensure the continuous and stable operation of the system; under stable working conditions, the variable step length hill climbing search method is used to realize high tracking accuracy MPPT control, which effectively balances the efficiency and stability of the system operation, significantly improves the overall efficiency of pressure difference power generation, fully utilizes gas pressure energy for efficient power generation, and improves the economic benefits of energy utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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 work.

[0034] Figure 1 A schematic diagram of the structure of a high-speed direct-drive pressure difference power generation system provided by the present invention;

[0035] Figure 2 A schematic diagram of the main circuit structure of a back-to-back dual PWM three-level converter provided by the present invention;

[0036] Figure 3 A schematic diagram of the vector control structure of a back-to-back dual PWM converter provided by the present invention;

[0037] Figure 4 A schematic diagram of a fundamental current loop control structure based on active resistance provided by the present invention;

[0038] Figure 5 The figure is an experimental result diagram of the fundamental current loop based on active resistance provided by the present invention;

[0039] Figure 6 A schematic diagram of a harmonic current loop control structure based on a QPR regulator provided by the present invention;

[0040] Figure 7 The instruction tracking effect diagram of the PI and QPR regulators provided by the present invention;

[0041] Figure 8 An efficiency-characteristic ratio graph of the expander provided by the present invention;

[0042] Fig. 9 A schematic diagram of the dual-mode pressure difference power generation MPPT algorithm flow provided by the present invention;

[0043] Fig.10 The motor output waveform diagram provided by the present invention;

[0044] Fig.11 The power grid related waveform diagram provided by the present invention;

[0045] Fig.12 A schematic diagram of gas operating conditions and speed tracking provided by the present invention;

[0046] Fig.13 The output waveform diagram of the expander provided by the present invention;

[0047] Fig.14 The relevant waveform diagram of the electromechanical link provided by the present invention;

[0048] Fig.15 A schematic flow chart of a control method for a high-speed dual three-phase permanent magnet synchronous generator provided by the present invention. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] See also Figure 1-Figure 13 The first aspect of the present invention provides a control method for a high-speed dual three-phase permanent magnet synchronous generator, comprising:

[0051] S1, using equal amplitude vector space decoupling and synchronous rotating coordinate transformation, the mathematical model of high-speed dual three-phase permanent magnet synchronous generator is constructed, and the gas-machine-electric coupling mathematical equation is obtained in combination with the output mechanical power expression of the expander shaft;

[0052] S2, a back-to-back dual PWM converter vector control method constructed based on the gas-machine-electric coupling mathematical equations to control the speed and current harmonics of the high-speed dual three-phase permanent magnet synchronous generator;

[0053] S3, optimizes the current loop and power quality of the high-speed dual three-phase permanent magnet synchronous generator by designing a fundamental current loop based on active resistance and a harmonic current loop based on quasi-proportional resonant regulator;

[0054] S4, using the dual-mode pressure difference power generation MPPT control strategy to control the output power of the high-speed dual three-phase permanent magnet synchronous generator, and obtaining a control method for the high-speed dual three-phase permanent magnet synchronous generator.

[0055] It should be noted that the expander in the present invention refers to a turbine expander, and the synchronous generator, generator or motor refers to a high-speed dual three-phase permanent magnet synchronous generator.

[0056] This embodiment designs a complex vector decoupling fundamental current loop based on active resistance and a harmonic current loop based on quasi-proportional resonant regulator to address the current coupling and harmonic problems of high-speed motors. Considering the time-sharing law of gas conditions and focusing on the characteristic ratio of the turbine expander, a dual-mode differential pressure power generation maximum power point tracking control strategy based on the optimal characteristic ratio is proposed to balance the efficiency and stability of the system operation under severe and stable gas conditions. The experimental results show the correctness and effectiveness of the system model and control strategy.

[0057] In this embodiment, the main structure of the high-speed direct-drive pressure difference power generation system is as follows: Figure 1 As shown, it consists of a turbine expander, a high-speed dual three-phase permanent magnet synchronous generator, a back-to-back dual PWM converter, a capacitor, a filter and a power grid.

[0058] Since the high-speed dual three-phase permanent magnet synchronous generator is a nonlinear high-dimensional model with strong coupling of multiple variables in the natural coordinate system, it is difficult to achieve high-performance control. Therefore, in this embodiment, the vector space decoupling (VSD) method is used to model the high-speed dual three-phase permanent magnet synchronous generator with 30° phase shift and neutral point isolation. Based on the equal amplitude VSD and synchronous rotating coordinate transformation, the mathematical model of the high-speed dual three-phase permanent magnet synchronous generator is obtained as follows:

[0059]

[0060] T e =3p[(L d -L q )i d +ψ f ]i q (2)

[0061]

[0062] In formulas (1)-(3), u d 、u q 、u x 、u y They represent the dq and xy components of the stator voltage respectively, i d 、i q 、i x 、i yRespectively represent the dq and xy components of the stator current, R s Indicates stator resistance, L d , L q , L z Represent dq inductance and self-leakage inductance respectively, w e represents the rotor electrical angular velocity, Ψ f represents the permanent magnet flux, p represents the number of rotor pole pairs, J represents the moment of inertia, B represents the damping coefficient, T e Represents electromagnetic torque, T m Represents mechanical torque.

[0063] According to the principles of engineering thermodynamics, the treatment of high-pressure gas by a turbo expander under ideal conditions can be regarded as an isentropic expansion process. Considering the operating efficiency of the turbo expander, the mechanical power output on the shaft can be expressed as:

[0064] Among them, W t represents the output power of the expander in kW, Δh represents the gas enthalpy drop in kJ / kg, Q represents the gas pipeline mass flow in kg / s, η t represents the efficiency of the expander, κ represents the constant entropy index of natural gas, R g represents the gas constant in kJ / (kg·K), T1 represents the inlet temperature in K, P1 represents the inlet pressure, and P2 represents the outlet pressure in MPa;

[0065] And the expression of natural gas constant entropy index κ is: Among them, C p It represents the specific heat capacity at constant pressure, which represents the heat required for the system to increase 1K during constant pressure, C v It is the specific heat capacity at constant volume, which represents the heat required for the system to increase 1K during the constant volume process.

[0066] In this embodiment, the gas-machine-electric model omits the reduction mechanism, and the turbine expander and the high-speed dual three-phase permanent magnet synchronous generator are connected to run, and the two have the same speed. There is no additional loss on the shaft except friction. Combining equations (2), (3) and (4), the shaft transmission relationship is:

[0067]

[0068] In the formula, w t is the mechanical angular velocity of the turboexpander working shaft, satisfying w t =w e / p, and thus the gas-machine-electric coupling mathematical equation (Equation (5)) is derived, which provides a theoretical basis for establishing a high-speed direct-drive pressure difference power generation system model.

[0069] The back-to-back dual PWM converter structure in this embodiment is as follows Figure 2 As shown, the motor side follows the convention of electric motors, and the grid side takes the output power as the positive direction; N1 and N2 represent the neutral points of the two sets of windings, N g Indicates the neutral point of the power grid; e A 、e B 、e C 、e U 、e V 、e W is the rotor induced electromotive force, e a 、e b 、e c is the three-phase grid voltage; u A 、u B 、u C 、u U 、u V 、u W is the stator six-phase terminal voltage, u a 、u b 、u c is the three-phase terminal voltage of the power grid; i A 、i B 、i C 、i U 、i V 、i W is the six-phase stator current, i a 、i b 、i b is the grid current; R s , L s is the stator resistance and inductance, R g , L g are the resistance and inductance of the grid; C1 and C2 are the upper and lower capacitors of the busbar.

[0070] In the high-speed direct-drive gas pressure difference power generation system, the turbine expander converts gas pressure energy into mechanical torque, and the conversion efficiency is closely related to the operating speed of the turbine expander. In order to maximize the efficiency of the turbine expander, the back-to-back dual PWM converter vector control method is used in this embodiment to achieve coordinated optimization control of the motor and the grid side. Specifically:

[0071] Back-to-back dual PWM converter vector control structure Figure 3As shown. On the motor side, it implements high-performance speed tracking for the coaxially connected high-speed dual three-phase permanent magnet synchronous generator with rotor flux orientation. Specifically, a high-speed dual three-phase permanent magnet synchronous generator vector control method based on VSD coordinate transformation is adopted. The outer loop uses PI to accurately track the generator speed, while the inner loop constructs a four-dimensional current loop with independent decoupling of the fundamental subspace and harmonic subspace. Four special regulators are used to implement closed-loop control of the fundamental current and harmonic current respectively, so as to ensure the stability and efficiency of the motor operation;

[0072] On the grid side, it is oriented to the grid voltage, with the goal of enabling the gas pressure difference power generation system to operate at unity power factor during the process of outputting electric energy to the grid. In specific operations, fixed base frequency control is implemented with bus voltage as the target, and a double closed-loop vector control structure consisting of a voltage outer loop and a current inner loop is used for cascaded control, and a PI controller is used for command tracking, thereby ensuring that electric energy is smoothly and high-qualityly incorporated into the grid, reducing the generation of reactive power, and improving the power quality and grid compatibility of the entire power generation system.

[0073] When the high-speed dual three-phase permanent magnet synchronous generator is running, the electromechanical energy conversion is mainly concentrated in the fundamental (ab) subspace, so the high-precision control of the fundamental current is crucial to the stable operation of the motor, which is the basic premise for the stable operation of the motor. At the same time, in order to reduce unnecessary losses in the system, the current components of the harmonic (uv) subspace must be effectively suppressed.

[0074] For fundamental current loop control, as shown in step S3 and Figure 4 The fundamental current loop control structure of the active resistor is shown, where the feedback gain coefficient Kar is the key setting value of the active resistor. In view of the strong current coupling problem under high-speed conditions, this embodiment adopts a complex vector decoupling design, and improves the parameter robustness of the current loop by adding active resistors, making it perform better in command tracking and disturbance suppression;

[0075] In the analysis process, the system delay is ignored, and the back electromotive force is used as the disturbance input. The amplitude-phase-frequency curve of the disturbance transfer function is plotted with different K ar The change of value, such as Figure 5 As shown. Figure 5 In the figure, when the fundamental frequency is 1000Hz, under the same bandwidth and motor parameter conditions, it can be clearly observed that the amplitude and phase change with K ar The disturbance suppression effect is more significant, especially near the fundamental frequency, which fully proves the effectiveness of adding active resistance to improve the anti-interference ability of the current loop. It should be pointed out that when K ar When =0, the amplitude at the fundamental frequency will increase in a spike-like manner, which clearly shows that the control performance of the conventional complex vector decoupling current loop at the fundamental frequency is obviously insufficient.

[0076] In terms of harmonic current loop control, such as step S3 and Figure 6 The harmonic current loop control structure of the quasi proportional resonant (QPR) regulator shown in the figure uses two resonators in cascade to implement zero reference value tracking control on the fifth and seventh harmonic currents with high content in the harmonic subspace;

[0077] In this embodiment, according to Figure 6 Establish the Simulink model of the harmonic current loop and set the proportional coefficient K P =1, integral coefficient K I =20, angular frequency coefficient w c =20, and a reference signal with five or seven sine waves superimposed at a fundamental frequency of 500Hz and an amplitude of 10A was simulated to verify the effectiveness of the QPR regulator. During the test, variables were strictly controlled to ensure that other experimental conditions, except for the regulator type, remained consistent in order to accurately compare the performance differences between the PI and QPR regulators;

[0078] Through real-time monitoring of the model operation and data, the dynamic response process and steady-state error of different regulators when tracking the reference signal are fully recorded, and then the command tracking effect of the two regulators is deeply analyzed. Then, the detailed comparison results of the steady-state waveforms of the command tracking of the high-frequency AC reference signal by the PI and QPR regulators under the same bandwidth and motor parameters are obtained, such as Figure 7 As shown:

[0079] from Figure 7 As can be seen in (a), under PI control, there is always an obvious error between the actual signal and the reference signal. This is because the gain of the PI regulator is limited in the high-frequency band, making it difficult to accurately track the rapidly changing high-frequency AC signal, resulting in a large deviation between the actual output and the expected reference signal.

[0080] and Figure 7 In (b), the tracking is slightly poor only at the peaks and troughs under QPR control. This is because the QPR regulator, through its unique resonant structure, can provide extremely high gain near a specific frequency, thereby effectively suppressing and tracking the fifth and seventh harmonic currents in the harmonic subspace. In contrast, the QPR regulator's tracking ability for high-frequency AC signals is significantly better than that of the PI regulator. It can respond to changes in the reference signal more quickly and accurately, reduce steady-state errors, and is more suitable for the harmonic subspace control of high-speed dual three-phase permanent magnet synchronous generators.

[0081] In the study of control strategies for gas pressure difference power generation systems, it is crucial to find an efficient maximum power point tracking (MPPT) method. Among them, the optimal characteristic ratio method uses expander parameters and real-time gas conditions to directly calculate the current theoretical optimal reference speed to achieve MPPT control. It only needs to extract real-time operating temperature, pressure, flow and other data from the original control system of the expander. It is easy to implement and has a fast response speed. In the optimal characteristic ratio method, the characteristic ratio of the expander Defined as the circumferential velocity u1 at the inlet of the working impeller and the isentropic ideal speed c of the expander s The ratio of

[0082]

[0083] In the formula, it is easy to know from the principle of dynamics that at unit mass flow rate c s satisfy

[0084] c s 2 =2Δh (7)

[0085] The circumferential speed u1 of the working impeller is related to the rotation speed n t The relationship is

[0086]

[0087] Thus, the expander characteristic ratio is obtained About speed n t The expression is

[0088]

[0089] Where n t is the operating speed of the turbo expander, in rpm; D1 is the working impeller diameter, in m.

[0090] From formula (9), we can see that when the working fluid state is constant, With n t However, due to the uncertainty of gas conditions and pipeline and mechanical losses, there is a specific optimal characteristic ratio. At this optimal characteristic ratio, the turboexpander can achieve maximum efficiency h tmax , and under the same operating conditions, the output power of the turbo expander can achieve the maximum value;

[0091] The efficiency-characteristic ratio curve of the turboexpander is shown in Figure 8In the figure, it can be seen that if point A is used as the starting working point, the expander is running at the best characteristic ratio and is in the state of maximum efficiency. However, when the gas operating conditions change, such as the actual flow rate Q increases relative to the rated flow rate Qn (Q>Qn), the original efficiency-characteristic ratio curve will shift accordingly, and the working point B corresponding to the current characteristic ratio will no longer meet the maximum efficiency requirements. In this case, it is necessary to adjust the speed of the motor to move the working point to the new maximum power point C. In this way, simple and efficient MPPT control can be achieved, thereby ensuring that the turbine expander can maintain high-efficiency operation as much as possible under different operating conditions and improve energy utilization efficiency.

[0092] In practical applications, the optimal characteristic ratio method has certain limitations. First, its efficiency-characteristic ratio curve must rely on accurate experimental data provided by the expander manufacturer to obtain. Once the environment changes or the equipment ages, the portability of the algorithm will become very poor. Secondly, because the actual high-pressure gas working conditions are extremely complex, the optimal characteristic ratio will change greatly, and the optimal reference speed will also fluctuate violently, which is not conducive to the speed regulation operation of the motor. Therefore, this method is not fully applicable to high-speed direct-drive pressure difference power generation.

[0093] The hill climbing search method applies a disturbance to the speed, then judges the power change before and after the disturbance, and repeats this search process until the maximum power point is reached, which effectively reduces the dependence on parameters, and the algorithm is relatively portable. However, the hill climbing search method also has obvious disadvantages. On the one hand, the climbing step length will limit the speed tracking rate; on the other hand, when the speed is disturbed, if the gas conditions change drastically, it is very easy to misjudge the direction of power change during the search process, making it difficult for the algorithm to continue to operate normally. Moreover, due to the presence of disturbances, the steady-state speed will fluctuate around the optimal speed.

[0094] Since the actual gas operating conditions are affected by the peak and valley of gas consumption by residents, the operating conditions are stable or violent, showing a distinct time-division law. Therefore, in this embodiment, a dual-mode differential pressure power generation MPPT control strategy combining the best characteristic ratio method with the variable step length hill climbing search method is proposed. The specific process is as follows: Fig. 9 Through this dual-mode control strategy, the maximum power point tracking of pressure difference power generation can be more effectively achieved under different gas conditions, thereby improving power generation efficiency and system stability.

[0095] Specifically, the dual-mode differential pressure power generation MPPT control strategy has different responses for different gas operating conditions. During periods when gas conditions change dramatically, i.e., peak gas usage for residents, the strategy uses the theoretical characteristic ratio to directly calculate the current optimal reference speed, thereby quickly implementing MPPT control and avoiding factors that may lead to misjudgment of the hill-climbing search direction.

[0096] During the period when the gas condition changes steadily, that is, during the period when the residential gas consumption is low, a variable step-size hill climbing search method based on the optimal characteristic ratio is used to achieve high-precision MPPT control; the step-size design principle is: when the system is far away from the maximum power point, fast tracking is pursued so that it can quickly approach the maximum power point; when the system is close to the maximum power point, zero steady-state error is pursued to ensure that it can operate stably near the maximum power point;

[0097] The specific perturbation step length design takes the change of the current optimal characteristic ratio relative to the theoretical characteristic ratio as the reference value, and the calculation formula is: In the formula, s is the step size factor, which is used to set the range of variation of the perturbation step size. When the reference value is large, it means that the system is far away from the maximum power point. At this time, a larger step size will be used to enable the system to quickly iterate to the vicinity of the maximum power point; when the reference value is small, it means that the system is close to the maximum power point, and a smaller step size will be used to stabilize the system near the maximum power point, thus achieving adaptive adjustment of the perturbation step size.

[0098] In this embodiment, the dual-mode pressure difference power generation MPPT control strategy makes full use of the typical parameter of the expander characteristic ratio and the advantages of accurate and easy-to-obtain system operating condition data, takes the change of gas operating conditions as the basis for judgment, and adopts the optimal characteristic ratio method and variable step size hill climbing search method under severe and stable conditions respectively to balance the efficiency and stability of the system operation, thereby obtaining a control method for a high-speed dual three-phase permanent magnet synchronous generator.

[0099] See also Figure 10-14 The second embodiment of the present invention provides a simulation experiment to verify the effectiveness of the dual-mode pressure difference power generation MPPT control algorithm under complex gas conditions:

[0100] The turbine expander is simulated by constant torque direct-drive power generation, and the turbine expander is connected to a high-speed dual three-phase permanent magnet synchronous generator to implement gas pressure difference power generation. The effectiveness of the dual-mode pressure difference power generation MPPT control algorithm under complex gas conditions is verified. By comparing the control performance with the conventional PI current loop, an active resistance current loop scheme that can improve current stability is obtained.

[0101] Specifically, the electromechanical control link is first effectively verified. In the electromechanical control link, the driving torque is directly given instead of the turbine expander. At the initial moment, the high-speed dual three-phase permanent magnet synchronous generator is driven to run with a rated torque of 10N·m. The reference speed is given to be 30000rpm and remains unchanged. At 0.6s, the driving torque is increased by about 1.5 times to simulate the disturbance condition, that is, the torque step is 15N·m. The total simulation time is 1s. The simulation results of the electromechanical link are as follows: Fig.10 and Fig.11 As shown;

[0102] from Fig.10 As shown in (a), the motor can quickly rise from a stationary state to 30,000 rpm, with an overshoot of about 125 rpm, and when the driving torque is disturbed, the speed only fluctuates slightly before quickly returning to a stable state; Fig.10 (b) shows the electromagnetic torque waveform according to the set driving torque change; Fig.10 (c) and (d) show the fundamental subspace and harmonic subspace currents of the high-speed dual three-phase permanent magnet synchronous generator, respectively. Under rated operation, their amplitudes are about 30A and 10A, respectively. Fig.10 (e) is the six-phase steady-state stator current waveform, with an amplitude of about 48A and good sinusoidal performance;

[0103] Depend on Fig.11 (a) It can be seen that the bus voltage is stably controlled at 800 V, and only a small fluctuation of about 10 V occurs when the speed slope changes; Fig.11 (b) is the three-phase current waveform of the power grid. Its amplitude changes from 42A to 72A during torque disturbance. Fig.11 (c) It can be seen that the phase difference between the phase voltage and phase current of phase a in the same reference direction is 180°, indicating that the power grid is in a state of absorbing power.

[0104] It can be seen from the above experimental results that in the simulation experiment of the electromechanical control link, the motor's starting and running performance is good, it has strong adaptability to the disturbance of the driving torque, can quickly restore the stable speed, and the current waveform and bus voltage are also relatively stable. This shows that when there is no actual effect of the gas pressure difference, the electromechanical control part of the system can effectively respond to certain operating conditions. Changes, laying the foundation for subsequent gas pressure difference power generation experiments.

[0105] In terms of gas pressure difference power generation, the turbine expander is connected to a high-speed dual three-phase permanent magnet synchronous generator to implement gas pressure difference power generation, and according to Fig. 9 To calculate the MPPT reference speed, compare the best characteristics of mode I to Set to 0.6, set the step factor s to 15000 in mode II, set the lower limit of the disturbance step Δn to 100rpm, the upper limit to 1000rpm, and set the initial reference speed to 3000rpm. In order to simulate the change of gas conditions, the intake pressure is selected as the variable, and P1 is set to 5.5MPa from 0 to 4s, and it starts to decrease linearly at 4s, stabilizes at 4.5MPa from 5 to 7s, and starts to increase linearly at 7s. After 8s, it stabilizes at the rated working condition of 5MPa. The entire simulation time is 10s. The simulation results of the gas pressure difference power generation system are shown in Figure 2. Fig.12 , Fig.13 and Fig.14 Show it.

[0106] Depend on Fig.12 (a) It can be seen that with the change of intake pressure, the gas enthalpy drop shows a power-exponential increase and decrease trend between 54.5 kJ / kg and 78.5 kJ / kg, thus forming a complex operating condition of alternating changes of "stable-sharp decrease-stable-sharp increase-rated"; according to Fig. 9 The designed dual-mode pressure difference power generation MPPT control strategy calculates the reference speed as follows Fig.12 As shown in (b), under stable working conditions, the system will enter working mode II, at which time a smaller step size is used to finely adjust the error between the actual speed and the reference speed, and stabilize near the optimal speed with the minimum step size. Under severe working conditions, it will enter working mode I, and the actual speed will quickly approach the optimal speed with the maximum disturbance step size;

[0107] Fig.13 (a) and (b) clearly show the characteristic ratio and efficiency change curve of the turbo expander. When the system works in mode I, the characteristic ratio is almost stable at the theoretical optimal value of 0.6, and the efficiency is about 81.7%. When the system works in mode II, the characteristic ratio is about 0.61, and the efficiency can reach the theoretical maximum value of 82%. Fig.13 (c) shows the torque waveforms of the generator and expander, which are significantly affected by changes in intake pressure.

[0108] Let's look at the relationship between voltage and current Fig.14 ,in Fig.14 (a) is the bus voltage waveform. When the system is started, it is in mode II. Due to the need to quickly approach the optimal working point, the reference speed will produce an obvious disturbance step, which will cause a certain degree of voltage fluctuation. Under severe working conditions, the speed disturbance change will also cause a small voltage fluctuation, but the bus voltage can generally be stably controlled at 800V. Fig.14 (b) shows the grid a phase current waveform, whose amplitude will change accordingly with the change of gas working conditions; Fig.14(c) It can be seen that under the rated (8 to 10s) working conditions, the motor output power is about 28kW and the grid absorption power is about 26.5kW. Since the harmonic subspace of the high-speed dual three-phase permanent magnet synchronous generator does not participate in the electromechanical energy conversion during the entire control process, there will be a certain power loss. However, the reactive power of the grid is always kept at zero, and the system can operate stably in the unity power factor state.

[0109] Through the detailed process and result analysis of the above-mentioned constant torque direct-drive power generation and gas pressure difference power generation, the effectiveness of the dual-mode pressure difference power generation MPPT control algorithm under complex gas conditions is fully verified, and by comparing with the conventional PI current loop control performance, the advantage of the active resistance current loop solution that can improve current stability of the present invention is strongly demonstrated.

[0110] Part of the data in the above formula is calculated by removing the dimension and taking its numerical value. The formula is a formula closest to the actual situation obtained by software simulation of a large amount of collected data; the preset parameters and preset thresholds in the formula are set by technical personnel in this field according to actual conditions or obtained through simulation of a large amount of data.

[0111] Working principle of the present invention:

[0112] The present invention establishes a gas-machine-electric integrated model based on a gas expander, constructs a back-to-back dual PWM converter vector control system, and designs an active resistance current loop for the current coupling and instability problems of a high-speed dual three-phase permanent magnet synchronous generator. Considering the time-division law of gas operating conditions and focusing on the characteristic ratio of the turbine expander, a dual-mode MPPT control strategy suitable for gas pressure difference power generation is proposed. The feasibility of the system model and control strategy is illustrated by two simulation modes: constant torque direct-drive power generation and gas pressure difference power generation. A pressure difference generator set experimental platform is built to verify the effectiveness of the dual-mode MPPT and active resistance current loop. The experimental results show that the dual-mode MPPT strategy can flexibly switch the tracking mode under complex conditions to achieve efficient and stable operation of pressure difference power generation; the active resistance current loop solution effectively improves the current stability and has good applicability to high-speed conditions.

[0113] The above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A control method for a high-speed dual three-phase permanent magnet synchronous generator, characterized in that: include: S1, using equal amplitude vector space decoupling and synchronous rotating coordinate transformation, the mathematical model of high-speed dual three-phase permanent magnet synchronous generator is constructed, and the gas-machine-electric coupling mathematical equation is obtained by combining the output mechanical power expression of the expander shaft; S2, a back-to-back dual PWM converter vector control method constructed based on the gas-machine-electric coupling mathematical equations to control the speed and current harmonics of the high-speed dual three-phase permanent magnet synchronous generator; S3, optimizes the current loop and power quality of the high-speed dual three-phase permanent magnet synchronous generator by designing a fundamental current loop based on active resistance and a harmonic current loop based on quasi-proportional resonant regulator; S4, using the dual-mode pressure difference power generation MPPT control strategy to control the output power of the high-speed dual three-phase permanent magnet synchronous generator, and obtaining a control method for the high-speed dual three-phase permanent magnet synchronous generator.

2. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The mathematical model of the high-speed dual three-phase permanent magnet synchronous generator is: Te=3p[(Ld-Lq)id+ψf]iq, Among them, u d 、u q 、u x 、u y They represent the dq and xy components of the stator voltage respectively, i d 、i q 、i x 、i y They represent the dq and xy components of the stator current respectively, and R s Indicates stator resistance, L d , L q , L z Represent dq inductance and self-leakage inductance respectively, w e represents the rotor electrical angular velocity, Ψ f represents the permanent magnet flux, p represents the number of rotor pole pairs, J represents the moment of inertia, B represents the damping coefficient, T e Represents electromagnetic torque, T m Represents mechanical torque.

3. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The output mechanical power expression of the expander shaft is: Among them, W t represents the output power of the expander in kW, Δh represents the gas enthalpy drop in kJ / kg, Q represents the gas pipeline mass flow in kg / s, η t represents the efficiency of the expander, κ represents the constant entropy index of natural gas, and C p is the specific heat capacity at constant pressure, C v is the specific heat capacity at constant volume, R g It represents the gas constant in kJ / (kg·K), T1 represents the inlet temperature in K, P1 represents the inlet pressure, and P2 represents the outlet pressure in MPa.

4. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1 is characterized in that: The gas-mechanical-electrical coupling mathematical equation is: Among them, w t represents the mechanical angular velocity of the expander working shaft, and w t =w e / p, t indicates time.

5. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The back-to-back dual PWM converter vector control method comprises: The motor-side converter uses rotor flux orientation to perform high-performance speed tracking on the coaxially connected high-speed dual three-phase permanent magnet synchronous generator: the high-speed dual three-phase permanent magnet synchronous generator vector control based on VSD coordinate transformation is adopted. The outer loop tracks the generator speed through PI, and the inner loop is a four-dimensional current loop with independent decoupling of the fundamental subspace and harmonic subspace. Four regulators are used to perform closed-loop control on the fundamental current and harmonic current respectively. The grid-side converter is oriented with the grid voltage so that the gas pressure difference power generation system outputs electric energy to the grid at a unity power factor: fixed base frequency control is implemented with the bus voltage as the target, and a double closed-loop vector control structure composed of a voltage outer loop and a current inner loop cascade is used to perform command tracking using a PI controller; wherein, the gas pressure difference power generation system includes: an expander, a high-speed dual three-phase permanent magnet synchronous generator, a back-to-back dual PWM converter, a capacitor, a filter and a grid.

6. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The feedback gain coefficient K of the fundamental current loop based on active resistance is ar , indicating the active resistance setting value.

7. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The control structure of the harmonic current loop includes using two resonator cascades to track and control the fifth harmonic current and the seventh harmonic current in the harmonic subspace.

8. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The dual-mode pressure difference power generation MPPT control strategy includes: During the peak period of gas consumption for residents, the optimal reference speed of the generator is calculated using the theoretical characteristic ratio, and the MPPT is controlled according to the optimal reference speed; During the off-peak period of residential gas consumption, the MPPT is controlled by using a variable step-size hill climbing search method based on the optimal characteristic ratio.

9. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The theoretical characteristic ratio is: in, represents the theoretical characteristic ratio, u1 represents the circumferential speed at the inlet of the expander impeller, c s represents the isentropic ideal speed of the expander, and c s 2 =2Δh,n t It indicates the operating speed of the expander in rpm; D1 indicates the diameter of the working impeller in m.

10. The control method of a high-speed dual three-phase permanent magnet synchronous generator according to claim 1, characterized in that: The variable step length hill climbing search method based on the optimal characteristic ratio is: According to the formula Get the step length △n; where s represents the step length factor, Indicates the best characteristic ratio.

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