Fast Frequency Support Control Method and System for Grid-Type Converters

Abstract

This invention provides a fast frequency support control method and system for a grid-type converter, comprising: Step S1: establishing a heterogeneous power system model, including a GFM converter model, a synchronous generator (SG) model, and a GFL wind turbine model; Step S2: based on the established GFL wind turbine model, treating the output power and load power of the GFL wind turbine as disturbances, and designing a preset time nonlinear observer to estimate the disturbances; Step S3: designing a preset time sliding mode controller to adjust the output power increment of the GFM converter to adjust the frequency of the heterogeneous power system; Step S4: simulating the suppression of oscillations by adjusting the frequency of the heterogeneous power system, and displaying the simulation results. This invention can demonstrate smaller overshoot and shorter convergence time.

Description

Technical Field

[0001] This invention relates to the field of distributed generation control technology for islanded AC microgrids, specifically to a fast frequency support control method and system for grid-connected converters. Background Technology

[0002] With the large-scale integration of renewable energy through power electronic devices, power systems are gradually transitioning to heterogeneous power systems. Therefore, heterogeneous power systems consist of different types of power sources, including traditional thermal power plants, grid-following (GFL) renewable energy fields, and grid-forming (GFM) energy storage power stations. However, the integration of renewable energy into the grid through power electronic devices reduces the system's rotational inertia, leading to rapid dynamic changes and significant frequency deviations when the heterogeneous power system is subjected to small disturbances. Therefore, studying the frequency stability of heterogeneous power systems is of great significance.

[0003] In heterogeneous power systems, renewable energy is integrated into the grid via GFL (Ground-Floating Unit) control, with the main grid maintaining synchronous operation. However, the inertia and frequency support capabilities provided by GFLs are relatively low. In traditional grids, frequency support mainly relies on synchronous generator governors. However, with the increasing penetration of renewable energy, the capacity of synchronous generators is decreasing, making it difficult to meet the inertia and frequency operation requirements. Furthermore, governors have slow response times, are prone to damage with frequent use, and struggle to achieve Fast Frequency Response (FFR).

[0004] In contrast, GFM energy storage technology, with its rapid response and strong regulation capabilities, has been used in power systems to address power gaps and provide inertia and frequency support. The control of GFM converters mainly includes droop control and Virtual Synchronous Generator (VSG) control, the latter providing inertia support by simulating the dynamic characteristics of a synchronous generator. However, frequency regulation still relies on droop control, which can lead to frequency deviations and limit the frequency support capability of GFM converters. Furthermore, the randomness of user electricity consumption behavior and the intermittency of renewable energy in heterogeneous power systems increase the uncertainty of active power supply, making frequency control a disturbance rejection problem. Observers can be used to estimate active power disturbances, but existing observers are mostly used in simple systems and are less applied to complex heterogeneous power systems with source-load uncertainties.

[0005] Preset-time stability can achieve system stability within a specified upper bound time, avoiding the problem of fixed-time stability convergence time depending on multiple parameters. Based on this, a preset-time observer is designed to estimate disturbances caused by source-load uncertainties in heterogeneous power systems. Sliding mode control (SMC) has attracted widespread attention due to its robustness to disturbances and parameter variations, simplicity of implementation, and fast response. Although SMC has been applied to transient stability and reactive power control in multi-machine power systems, its preset-time stability control in complex heterogeneous power systems has not been widely studied. This is mainly due to factors such as system heterogeneity, uncertainty, time delay effects, and high computational complexity, which make it difficult for traditional SMC methods to effectively address these challenges, thus limiting its application in such systems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fast frequency support control method and system for grid-type converters.

[0007] According to the present invention, a fast frequency support control method and system for a grid-type converter is provided, the scheme of which is as follows:

[0008] In a first aspect, a fast frequency support control method for a grid-type converter is provided, the method comprising:

[0009] Step S1: Establish a heterogeneous power system model, including the GFM converter model, the synchronous generator SG model, and the GFL wind turbine model;

[0010] Step S2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances.

[0011] Step S3: Design a preset time sliding mode controller to adjust the output power increment ΔP of the GFM converter. ref To regulate the frequency of heterogeneous power systems;

[0012] Step S4: Simulate the suppression of oscillations by adjusting the frequency of the heterogeneous power system, and display the simulation results.

[0013] Preferably, in step S1, the heterogeneous power system model is divided into two interconnected regions, namely region A and region B, which exchange power through tie lines;

[0014] The GFM converter includes a power control loop, a voltage control loop, and a current control loop. The power control loop regulates and synchronizes the output power with the grid. Within the power control loop, VSG control is used to regulate active power to achieve inertia and frequency support. Reactive power regulation and output voltage control at the point of common coupling (PCC) are accomplished through droop control within the power control loop. The GFM converter model is as follows:

[0015]

[0016] P1 = P AB +P L1 -P ω1 (2)

[0017] Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 This represents the output power of the GFL wind turbine generator set in region A.

[0018] Preferably, in step S1, a synchronous generator SG model is established:

[0019]

[0020] P2 = P L2 -P AB -P ω2 (4)

[0021] Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; P L2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B.

[0022] Preferably, the GFL wind turbine model is established in step S1 as follows:

[0023] The mechanical power generated by a GFL wind turbine is expressed as:

[0024]

[0025] The mechanical torque of a GFL wind turbine is expressed as follows:

[0026]

[0027] Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C p Represented as:

[0028]

[0029] The tip speed ratio λ is expressed as:

[0030]

[0031] By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached; a maximum power point tracking (MPPT) strategy is implemented to capture maximum wind energy; the maximum mechanical power of the wind turbine is expressed as follows:

[0032]

[0033] Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient;

[0034] In heterogeneous power systems, wind turbines are connected to the grid in the form of GFLs;

[0035] Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as:

[0036]

[0037] in, The frequency representing the center of inertia (COI); P ω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively. u=ΔP ref , H Σ =H1+H2, D Σ =D1+D2 represents the total damping coefficient of the system.

[0038] Preferably, step S2 includes:

[0039] The design support system is as follows:

[0040]

[0041] Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system;

[0042] The pre-designed time nonlinear observer is as follows:

[0043]

[0044] in, This is an estimate of the disturbance d. Let e ​​be the estimated value of state e. This represents the rate of change of the frequency error; Represented as:

[0045]

[0046] in, The sign function sig(·) represents the frequency estimation error. γ =sign(·)|·| γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

[0047] Preferably, step S3 includes:

[0048] The preset time sliding surface design is as follows:

[0049]

[0050] Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant;

[0051] When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get:

[0052]

[0053] Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for:

[0054]

[0055] Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is:

[0056]

[0057] Wherein, the controller coefficient is T c3 This represents the preset time constant of the equivalent controller;

[0058] Based on equations (16) and (17), the preset time sliding mode controller is designed as follows:

[0059]

[0060] Under the observer-based preset time sliding mode controller, the control error σ reaches the preset time sliding surface and converges to 0 within a preset time.

[0061] Secondly, a fast frequency support control system for a grid-type converter is provided, the system comprising:

[0062] Module M1: Establish heterogeneous power system models, including GFM converter model, synchronous generator SG model, and GFL wind turbine model;

[0063] Module M2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances.

[0064] Module M3: Design a preset time sliding mode controller to adjust the output power increment ΔP of the GFM converter. ref To regulate the frequency of heterogeneous power systems;

[0065] Module M4: Simulates the suppression of oscillations by adjusting the frequency of a heterogeneous power system and displays the simulation results.

[0066] Preferably, in module M1, the heterogeneous power system model is divided into two interconnected regions, namely region A and region B, which exchange power through tie lines;

[0067] The GFM converter includes a power control loop, a voltage control loop, and a current control loop. The power control loop regulates and synchronizes the output power with the grid. Within the power control loop, VSG control is used to regulate active power to achieve inertia and frequency support. Reactive power regulation and output voltage control at the point of common coupling (PCC) are accomplished through droop control within the power control loop. The GFM converter model is as follows:

[0068]

[0069] P1 = P AB +P L1 -P ω1 (2)

[0070] Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 The output power of the GFL wind turbine generators in region A;

[0071] A synchronous generator SG model is established in module M1:

[0072]

[0073] P2 = P L2 -P AB -P ω2 (4)

[0074] Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; P L2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B.

[0075] The GFL wind turbine model established in module M1 is as follows:

[0076] The mechanical power generated by a GFL wind turbine is expressed as:

[0077]

[0078] The mechanical torque of a GFL wind turbine is expressed as follows:

[0079]

[0080] Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C pRepresented as:

[0081]

[0082] The tip speed ratio λ is expressed as:

[0083]

[0084] By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached; a maximum power point tracking (MPPT) strategy is implemented to capture maximum wind energy; the maximum mechanical power of the wind turbine is expressed as follows:

[0085]

[0086] Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient;

[0087] In heterogeneous power systems, wind turbines are connected to the grid in the form of GFLs;

[0088] Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as:

[0089]

[0090] in, The frequency representing the center of inertia (COI); P ω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively. u=ΔP ref , H Σ =H1+H2, D Σ =D1+D2 represents the total damping coefficient of the system.

[0091] Preferably, the module M2 includes:

[0092] The design support system is as follows:

[0093]

[0094] Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system;

[0095] The pre-designed time nonlinear observer is as follows:

[0096]

[0097] in, This is an estimate of the disturbance d. Let e ​​be the estimated value of state e. This represents the rate of change of the frequency error; Represented as:

[0098]

[0099] in, The sign function sig(·) represents the frequency estimation error. γ =sign(·)|·| γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

[0100] Preferably, the module M3 includes:

[0101] The preset time sliding surface design is as follows:

[0102]

[0103] Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant;

[0104] When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get:

[0105]

[0106] Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for:

[0107]

[0108] Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is:

[0109]

[0110] Wherein, the controller coefficient is T c3This represents the preset time constant of the equivalent controller;

[0111] Based on equations (16) and (17), the preset time sliding mode controller is designed as follows:

[0112]

[0113] Under the observer-based preset time sliding mode controller, the control error σ reaches the preset time sliding surface and converges to 0 within a preset time.

[0114] Compared with the prior art, the present invention has the following beneficial effects:

[0115] 1. By designing a control strategy based on a preset time sliding mode observer, this invention achieves rapid estimation of source-load uncertainty disturbances in heterogeneous power systems, overcoming the limitations of traditional observers' convergence time-dependent parameters;

[0116] 2. This invention effectively suppresses system frequency oscillations within a preset time by using a preset time sliding mode controller, reducing frequency overshoot and convergence time. Compared with traditional SMC and PI control methods, it significantly improves the dynamic response performance of the system.

[0117] 3. Combining the robustness of sliding mode control, this invention can cope with source-load uncertainties and external disturbances in complex heterogeneous power systems, ensuring system frequency stability;

[0118] 4. By rapidly regulating the active power of the grid-type converter, this invention effectively solves the problem of insufficient frequency regulation capability in heterogeneous power systems, and provides efficient inertia and frequency support.

[0119] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description

[0120] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0121] Figure 1 This is an overall framework diagram of the present invention;

[0122] Figure 2 This is the heterogeneous power system model of the present invention;

[0123] Figure 3 This is the control structure of the GFM converter of the present invention;

[0124] Figure 4 shows the simulation results of this invention. Detailed Implementation

[0125] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0126] This invention provides a fast frequency support control (SMC) method for grid-connected converters. By improving the SMC control strategy and customizing the design for the characteristics of heterogeneous power systems, it successfully overcomes the aforementioned difficulties, achieving effective control of preset time stability. This significantly improves the system's stability and dynamic response performance, demonstrating the application potential and innovative value of this method in complex power systems. (Refer to...) Figure 1 As shown, the invention includes:

[0127] Step S1: Establish a heterogeneous power system model, including the GFM converter model, the synchronous generator SG model, and the GFL wind turbine model;

[0128] Step S2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances.

[0129] Step S3: Design a preset time sliding mode controller to adjust the output power increment ΔP of the GFM converter. ref To regulate the frequency of heterogeneous power systems;

[0130] Step S4: Simulate the suppression of oscillations by adjusting the frequency of the heterogeneous power system, and display the simulation results.

[0131] 1) Establish a heterogeneous power system model, details of which are as follows:

[0132] Figure 2 This invention presents a heterogeneous power system model, comprising a synchronous generator (SG), a GFL wind turbine generator, and a GFM converter. The heterogeneous power system includes two interconnected regions, region A and region B, which exchange power via a tie line. The models of each component are established as follows.

[0133] Figure 3The control structure of the GFM converter is illustrated, comprising three control loops: a power control loop, a voltage control loop, and a current control loop, which together constitute the control system of the GFM converter. The power control loop is primarily used to regulate and synchronize the output power (active and reactive power) with the grid. In the power control loop, VSG control is used to achieve inertia and frequency support, which is accomplished by regulating active power. Reactive power regulation and output voltage control at the point of common coupling (PCC) are achieved through droop control within the power control loop. Therefore, the model of the GFM converter can be described as follows:

[0134]

[0135] P1 = P AB +P L1 -P ω1 (2)

[0136] Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 This represents the output power of the GFL wind turbine generator set in region A.

[0137] Establish the dynamic equation model of the synchronous generator:

[0138]

[0139] P2 = P L2 -P AB -P ω2 (4)

[0140] Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; P L2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B.

[0141] Establish a GFL wind turbine model, and express the mechanical power generated by the GFL wind turbine as follows:

[0142]

[0143] The mechanical torque of a GFL wind turbine is expressed as follows:

[0144]

[0145] Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C p Represented as:

[0146]

[0147] The tip speed ratio λ is expressed as:

[0148]

[0149] By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached. Therefore, a Maximum Power Point Tracking (MPPT) strategy can be implemented to capture maximum wind energy. The maximum mechanical power of a wind turbine is expressed as follows:

[0150]

[0151] Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient;

[0152] In heterogeneous power systems, wind turbines are connected to the grid as GFLs; therefore, GFL wind turbines cannot provide inertia and operate in MPPT mode. Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as:

[0153]

[0154] in, The frequency representing the center of inertia (COI); P ω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively.

[0155]

[0156] H Σ =H1+H2, DΣ =D1+D2 represents the total damping coefficient of the system.

[0157] 2) Design a preset time nonlinear observer, details of which are as follows:

[0158] As shown in equation (10), the output power and load power of the GFL wind turbine are considered as disturbances, taking into account the randomness of the output power of the GFL wind turbine and the fluctuation of the load. Therefore, an observer needs to be designed to estimate the disturbance d.

[0159] First, the auxiliary system is designed as follows:

[0160]

[0161] Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system;

[0162] The pre-designed time nonlinear observer is as follows:

[0163]

[0164] in, This is an estimate of the disturbance d. Let e ​​be the estimated value of state e. This represents the rate of change of the frequency error; Represented as:

[0165]

[0166] in, The sign function sig(·) represents the frequency estimation error. γ =sign(·)|·| γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

[0167] The preset time observer proposed in this invention can estimate the disturbance d within a preset time, especially the output power and load power of the GFL wind turbine.

[0168] 3) Design a preset time sliding mode controller, details of which are as follows:

[0169] To allow the designed controller to regulate the output power increment ΔP of the GFM converter ref This is to regulate the frequency of heterogeneous power systems, thereby providing frequency support for them.

[0170] First, the preset time sliding surface is designed as follows:

[0171]

[0172] Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant;

[0173] When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get:

[0174]

[0175] Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for:

[0176]

[0177] Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is:

[0178]

[0179] Wherein, the controller coefficient is T c3 This represents the preset time constant of the equivalent controller;

[0180] Based on equations (16) and (17), the preset time sliding mode controller is designed as follows:

[0181]

[0182] Under the proposed observer-based preset time sliding mode controller (PTOBSMC), the control error σ can reach the preset time sliding surface and converge to 0 within a preset time.

[0183] The fast frequency support control framework for the grid-type converter based on a preset time sliding mode observer is referenced. Figure 1 As shown.

[0184] 4) Simulation results:

[0185] Table I Parameters of Heterogeneous Power Systems

[0186]

[0187] Based on the predetermined time theory and pre-selected parameters, the predetermined time is determined to be T. c1 =T c2 =1, and the relevant parameters are set as ρ=10, γ=0.2, k1=k4=k7=10, k2=k5=k8=5.4, k3=k6=k9=5.2.

[0188] Simulation Case: Load Variation

[0189] At t = 2s, a power of 6 × 10⁶ is disconnected from the system. 6 A load of W is connected, and at t=7s, a power of 8×10 6 The load is W. Simulation results show that regardless of whether the load is connected or disconnected, the frequency ω... COI Oscillations can occur at ω1 and ω2. However, in heterogeneous power systems, these oscillations can be effectively suppressed by adjusting the active power of the GFM energy storage system under the proposed observer-based preset-time sliding mode controller. Furthermore, compared to traditional SMC and PI control methods, the system exhibits smaller overshoot and shorter convergence time under the proposed observer-based preset-time sliding mode controller. Simulation results are shown in Figure 4.

[0190] This invention also provides a fast frequency support control system for a grid-type converter. This system can be implemented by executing the steps of the fast frequency support control method for the grid-type converter. That is, those skilled in the art can understand the fast frequency support control method for the grid-type converter as a preferred embodiment of the fast frequency support control system. The system specifically includes:

[0191] Module M1: Establish heterogeneous power system models, including GFM converter model, synchronous generator SG model, and GFL wind turbine model;

[0192] Module M2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances.

[0193] Module M3: Design a preset time sliding mode controller to adjust the output power increment ΔP of the GFM converter. ref To regulate the frequency of heterogeneous power systems;

[0194] Module M4: Simulates the suppression of oscillations by adjusting the frequency of a heterogeneous power system and displays the simulation results.

[0195] 1) Establish a heterogeneous power system model, details of which are as follows:

[0196] Figure 2This invention presents a heterogeneous power system model, comprising a synchronous generator (SG), a GFL wind turbine generator, and a GFM converter. The heterogeneous power system includes two interconnected regions, region A and region B, which exchange power via a tie line. The models of each component are established as follows.

[0197] Figure 3 The control structure of the GFM converter is illustrated, comprising three control loops: a power control loop, a voltage control loop, and a current control loop, which together constitute the control system of the GFM converter. The power control loop is primarily used to regulate and synchronize the output power (active and reactive power) with the grid. In the power control loop, VSG control is used to achieve inertia and frequency support, which is accomplished by regulating active power. Reactive power regulation and output voltage control at the point of common coupling (PCC) are achieved through droop control within the power control loop. Therefore, the model of the GFM converter can be described as follows:

[0198]

[0199] P1 = P AB +P L1 -P ω1 (2)

[0200] Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 This represents the output power of the GFL wind turbine generator set in region A.

[0201] Establish the dynamic equation model of the synchronous generator:

[0202]

[0203] P2 = P L2 -P AB -P ω2 (4)

[0204] Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; PL2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B.

[0205] Establish a GFL wind turbine model, and express the mechanical power generated by the GFL wind turbine as follows:

[0206]

[0207] The mechanical torque of a GFL wind turbine is expressed as follows:

[0208]

[0209] Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C p Represented as:

[0210]

[0211] The tip speed ratio λ is expressed as:

[0212]

[0213] By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached. Therefore, a Maximum Power Point Tracking (MPPT) strategy can be implemented to capture maximum wind energy. The maximum mechanical power of a wind turbine is expressed as follows:

[0214]

[0215] Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient;

[0216] In heterogeneous power systems, wind turbines are connected to the grid as GFLs; therefore, GFL wind turbines cannot provide inertia and operate in MPPT mode. Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as:

[0217]

[0218] in, The frequency representing the center of inertia (COI); Pω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively.

[0219] u=ΔP ref , H Σ =H1+H2, D Σ =D1+D2 represents the total damping coefficient of the system.

[0220] 2) Design a preset time nonlinear observer, details of which are as follows:

[0221] As shown in equation (10), the output power and load power of the GFL wind turbine are considered as disturbances, taking into account the randomness of the output power of the GFL wind turbine and the fluctuation of the load. Therefore, an observer needs to be designed to estimate the disturbance d.

[0222] First, the auxiliary system is designed as follows:

[0223]

[0224] Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system;

[0225] The pre-designed time nonlinear observer is as follows:

[0226]

[0227] in, This is an estimate of the disturbance d. Let e ​​be the estimated value of state e. This represents the rate of change of the frequency error; Represented as:

[0228]

[0229] in, The sign function sig(·) represents the frequency estimation error. γ =sign(|·|) γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

[0230] The preset time observer proposed in this invention can estimate the disturbance d within a preset time, especially the output power and load power of the GFL wind turbine.

[0231] 3) Design a preset time sliding mode controller, details of which are as follows:

[0232] To allow the designed controller to regulate the output power increment ΔP of the GFM converter ref This is to regulate the frequency of heterogeneous power systems, thereby providing frequency support for them.

[0233] First, the preset time sliding surface is designed as follows:

[0234]

[0235] Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant;

[0236] When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get:

[0237]

[0238] Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for:

[0239]

[0240] Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is:

[0241]

[0242] Wherein, the controller coefficient is T c3 This represents the preset time constant of the equivalent controller;

[0243] Based on equations (16) and (17), the preset time sliding mode controller is designed as follows:

[0244]

[0245] Under the proposed observer-based preset time sliding mode controller (PTOBSMC), the control error σ can reach the preset time sliding surface and converge to 0 within a preset time.

[0246] The fast frequency support control framework for the grid-type converter based on a preset time sliding mode observer is referenced. Figure 1As shown.

[0247] 4) Simulation results:

[0248] Table I Parameters of Heterogeneous Power Systems

[0249]

[0250] Based on the predetermined time theory and pre-selected parameters, the predetermined time is determined to be T. c1 =T c2 =1, and the relevant parameters are set as ρ=10, γ=0.2, k1=k4=k7=10, k2=k5=k8=5.4, k3=k6=k9=5.2.

[0251] Simulation Case: Load Variation

[0252] At t = 2s, a power of 6 × 10⁶ is disconnected from the system. 6 A load of W is connected, and at t=7s, a power of 8×10 6 The load is W. Simulation results show that regardless of whether the load is connected or disconnected, the frequency ω... COI Oscillations occur at ω1 and ω2, but in heterogeneous power systems, these oscillations can be effectively suppressed by adjusting the active power of the GFM energy storage system under the proposed observer-based preset-time sliding mode controller. Furthermore, compared to traditional SMC and PI control methods, the system exhibits smaller overshoot and shorter convergence time under the proposed observer-based preset-time sliding mode controller. Simulation results are referenced. Figures 4a-4d As shown.

[0253] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0254] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A fast frequency support control method for a grid-type converter, characterized in that, include: Step S1: Establish a heterogeneous power system model, including a GFM converter model, a synchronous generator SG model, and a GFL wind turbine model; Step S2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances. Step S3: Design a preset time sliding mode controller to adjust the output power increment of the GFM converter in order to regulate the frequency of the heterogeneous power system; Step S4: Simulate the suppression of oscillations by adjusting the frequency of the heterogeneous power system, and display the simulation results.

2. The fast frequency support control method for a grid-type converter according to claim 1, characterized in that, In step S1, the heterogeneous power system model is divided into two interconnected regions, namely region A and region B, which exchange power through tie lines. The GFM converter includes a power control loop, a voltage control loop, and a current control loop. The power control loop regulates and synchronizes the output power with the grid. Within the power control loop, VSG control is used to regulate active power to achieve inertia and frequency support. Reactive power regulation and output voltage control at the point of common coupling (PCC) are accomplished through droop control within the power control loop. The GFM converter model is as follows: P1=P AB +P L1 -P ω1 (2) Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 This represents the output power of the GFL wind turbine generator set in region A.

3. The fast frequency support control method for a grid-type converter according to claim 2, characterized in that, In step S1, a synchronous generator SG model is established: P2=P L2 -P AB -P ω2 (4) Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; P L2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B.

4. The fast frequency support control method for a grid-type converter according to claim 1, characterized in that, The GFL wind turbine model established in step S1 is as follows: The mechanical power generated by a GFL wind turbine is expressed as: The mechanical torque of a GFL wind turbine is expressed as follows: Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C p Represented as: The tip speed ratio λ is expressed as: By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached; a maximum power point tracking (MPPT) strategy is implemented to capture maximum wind energy; the maximum mechanical power of the wind turbine is expressed as follows: Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient; In heterogeneous power systems, wind turbines are connected to the grid in the form of GFLs; Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as: in, The frequency representing the center of inertia (COI); P ω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively. H Σ =H1+H2, D Σ =D1+D2 represents the total damping coefficient of the system.

5. The fast frequency support control method for a grid-type converter according to claim 4, characterized in that, Step S2 includes: The design support system is as follows: Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system; The pre-designed time nonlinear observer is as follows: in, This is an estimate of the disturbance d. Let e ​​be the estimated value of state e. This represents the rate of change of the frequency error; Represented as: in, The sign function sig(·) represents the frequency estimation error. γ =sign(·)|·| γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

6. The fast frequency support control method for a grid-type converter according to claim 1, characterized in that, Step S3 includes: The preset time sliding surface design is as follows: Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant; When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get: Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for: Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is: Wherein, the controller coefficient is T c3 This represents the preset time constant of the equivalent controller; Based on equations (16) and (17), the preset time sliding mode controller is designed as follows: Under the observer-based preset time sliding mode controller, the control error σ reaches the preset time sliding surface and converges to 0 within a preset time.

7. A fast frequency support control system for a grid-type converter, characterized in that, include: Module M1: Establish heterogeneous power system models, including GFM converter model, synchronous generator SG model, and GFL wind turbine model; Module M2: Based on the established GFL wind turbine model, the output power and load power of the GFL wind turbine are regarded as disturbances, and a preset time nonlinear observer is designed to estimate the disturbances. Module M3: Design a preset time sliding mode controller to adjust the output power increment of the GFM converter in order to regulate the frequency of the heterogeneous power system; Module M4: Simulates the suppression of oscillations by adjusting the frequency of a heterogeneous power system and displays the simulation results.

8. The fast frequency support control system for a grid-type converter according to claim 7, characterized in that, In module M1, the heterogeneous power system model is divided into two interconnected regions, namely region A and region B, which exchange power through tie lines. The GFM converter includes a power control loop, a voltage control loop, and a current control loop. The power control loop regulates and synchronizes the output power with the grid. Within the power control loop, VSG control is used to regulate active power to achieve inertia and frequency support. Reactive power regulation and output voltage control at the point of common coupling (PCC) are accomplished through droop control within the power control loop. The GFM converter model is as follows: P1=P AB +P L1 -P ω1 (2) Where ω1 is the frequency of the GFM converter; ω n The rated frequency; δ1 represents the power angle; t represents time; ΔP ref P represents the increment of the reference power. ref P1 and P1 represent the initial active power and output active power, respectively; D1 represents the damping coefficient of the GFM converter; H1 represents the inertial time constant of the GFM converter; P AB P represents the exchange power between region A and region B. L1 P is the load power of load 1. ω1 The output power of the GFL wind turbine generators in region A; A synchronous generator SG model is established in module M1: P2=P L2 -P AB -P ω2 (4) Among them, δ2,ω2,P2,D2,H2 and P m0 These represent the rotor angle, rotor speed, electromagnetic torque, damping coefficient of the synchronous generator, inertial time constant of the synchronous generator, and mechanical torque, respectively; P L2 P is the load power of load 2. ω2 This represents the output power of the GFL wind turbine generators in region B. The GFL wind turbine model established in module M1 is as follows: The mechanical power generated by a GFL wind turbine is expressed as: The mechanical torque of a GFL wind turbine is expressed as follows: Where ρ, ω, R and v ω These represent air density, mechanical rotation speed, rotor radius, and wind speed, respectively; C p λ and θ represent the tip speed ratio, wind energy utilization coefficient, and blade pitch angle, respectively; the wind energy utilization coefficient C p Represented as: The tip speed ratio λ is expressed as: By using equations (7) and (8), it was observed that when the pitch angle θ remains constant, the wind energy utilization coefficient C p The maximum value is reached; a maximum power point tracking (MPPT) strategy is implemented to capture maximum wind energy; the maximum mechanical power of the wind turbine is expressed as follows: Where, λ opt and ω opt These represent the optimal tip speed ratio and the optimal mechanical speed, respectively; C pmax This represents the maximum value of the wind energy utilization coefficient; In heterogeneous power systems, wind turbines are connected to the grid in the form of GFLs; Based on equations (1)-(4) and (9), the heterogeneous power system model is expressed as: in, The frequency representing the center of inertia (COI); P ω1 and P ω2 These represent the output power of wind turbine generator set 1 and wind turbine generator set 2, respectively. u=ΔP ref , H Σ =H1+H2, D Σ =D1+D2 represents the total damping coefficient of the system.

9. The fast frequency support control system for a grid-type converter according to claim 7, characterized in that, The module M2 includes: The design support system is as follows: Wherein, the frequency error e = ω COI -η, where ρ is a positive constant and η represents the auxiliary state variable of the system; The pre-designed time nonlinear observer is as follows: in, This is an estimate of the disturbance d. This is an estimate of state e. This represents the rate of change of the frequency error; Represented as: in, The sign function sig(·) represents the frequency estimation error. γ =sign(·)|·| γ Observer coefficients α1>0, α2>0, and preset time T c1 >0, T c1 This represents the preset time constant of the observer.

10. The fast frequency support control system for a grid-type converter according to claim 7, characterized in that, The module M3 includes: The preset time sliding surface design is as follows: Where σ=ω COI -ω n Represents control error, controller coefficient T c2 This represents the controller's preset time constant; When the control error σ reaches the preset time sliding surface, s = 0 is achieved. Therefore, we get: Based on the observation results of (10) and (15) and the preset time observer Obtain the equivalent controller u eq for: Let the approach controller be denoted as u. ri This is used to ensure that the control error σ effectively reaches the preset time sliding surface specified in equation (14), and its expression is: Wherein, the controller coefficient is T c3 This represents the preset time constant of the equivalent controller; Based on equations (16) and (17), the preset time sliding mode controller is designed as follows: Under the observer-based preset time sliding mode controller, the control error σ reaches the preset time sliding surface and converges to 0 within a preset time.

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