Event-triggered active-disturbance-rejection frequency control method of offshore wind power flexible direct-current grid-connected system

Abstract

The invention relates to an event-triggered active-disturbance-rejection frequency control method for an offshore wind power flexible direct-current grid-connected system, and belongs to the technical field of frequency stability control of a novel power system. Comprising the following steps: constructing an LFC model of an offshore wind plant through a flexible direct current power transmission grid-connected system; constructing a multi-region system model containing offshore wind power flexible direct current grid connection; according to a sampling sequence of an ADRC controller in the multi-region interconnection system, a continuous event triggering mechanism is combined, and a triggering condition is designed; the method comprises the following steps: designing an extended state observer according to an ACE signal output by an interconnection system, and designing an ET-ADRC control law to obtain an ET-ADRC controller; according to the characteristics of active output fluctuation of an offshore wind power plant and load disturbance of a system, an LFC model under mixed disturbance is constructed, and ET-ADRC is applied to an offshore wind power flexible direct current grid-connected system; and finally, a simulation experiment verifies that any unknown disturbance of the offshore wind power flexible direct current grid-connected system can be effectively inhibited, and meanwhile, the dynamic response performance of the control system is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of frequency stability control of novel power systems, and in particular relates to an event-triggered self-disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system. Background Art

[0002] With the transformation of the global energy structure and the rapid development of renewable energy, offshore wind power, as a clean and renewable energy form, is gradually becoming an important pillar in the energy field. The development of onshore wind power in my country has been relatively saturated, and the development of offshore wind power is an important direction for the transformation of my country's energy architecture. Stable offshore resources and the developed economy of coastal areas have created a good environment for the development of offshore wind power in my country. However, the offshore wind farm flexible direct current transmission (Voltage Source Converter based High Voltage Direct Current Transmission, hereinafter referred to as VSC-HVDC) grid-connected system faces challenges such as frequency fluctuations, poor stability, and high maintenance costs in actual operation, which seriously restricts its large-scale application and development.

[0003] Most of the existing frequency control methods for offshore wind power grid connection are primary frequency regulation control methods. Lu et al. proposed a coordinated control strategy for offshore wind farms in the document “Zongxiang, Lu, Ying Ye, Ying Qiao. An Adaptive Frequency Regulation Method With Grid-Friendly Restoration for VSC-HVDC Integrated Offshore Wind Farms [J]. IEEE Transactions on Power System. 2019, 34 (5): 3582-93”. They used the capacity of the standby units in the offshore wind farm to fill the power reduction after frequency regulation. Yang et al. proposed a coordinated control strategy for offshore wind power systems combined with a virtual inertia control strategy for wind turbines in the document “Yang Jingang, Yuan Zhichang, Li Shunxin, et al. Frequency control strategy for large wind farms connected to the grid via flexible DC transmission [J]. Electric Power Automation Equipment, 2019, 39 (06): 109-114”. At the same time, the VSC-HVDC grid-side converter station uses DC capacitor virtual inertia control, which effectively improves the inertial response capability of the interconnected power grid system.

[0004] The above methods are all based on the primary frequency regulation strategy of the virtual inertia of wind turbines. However, when the load fluctuates greatly, the frequency deviation exceeds a certain range, and the frequency deviation cannot be stabilized to 0 by relying solely on primary frequency regulation. For systems with large load fluctuations, it is often not enough to rely on primary frequency regulation to achieve complete frequency recovery. Therefore, the study of the event-triggered active disturbance rejection control (ET-ADRC) load frequency control (LFC) strategy of the offshore wind farm connected to the grid via the VSC-HVDC system can ensure the normal operation of the equipment, ensure the safety and stability of the power grid, and improve the anti-interference ability of the system, which has important practical significance and application value. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and to provide an event-triggered self-disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system, and an event-triggered self-disturbance rejection load frequency control method for controlling frequency stability. This method achieves effective suppression of frequency fluctuations in the offshore wind power flexible direct current grid-connected system, while taking into account the dynamic response performance of the control system.

[0006] To achieve the above object, the technical solution of the present invention is: an event-triggered automatic disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system, comprising:

[0007] S1. Construct the LFC model of the offshore wind farm connected to the grid via flexible direct current;

[0008] S2. Based on the dynamic equations of the system states expressed by each region in the interconnected system including offshore wind farms connected to the grid via flexible direct current transmission, a multi-region system model including offshore wind farms connected to the grid via flexible direct current transmission is constructed;

[0009] S3. Design the triggering conditions of the continuous event triggering mechanism based on the sampling sequence of the ADRC controller in the multi-region interconnected power system and the continuous event triggering mechanism;

[0010] S4. Design an extended state observer based on the ACE signal output by the interconnected power system, and on this basis, design a control law for continuous event-triggered ADRC to obtain an event-triggered ADRC controller, namely, an ET-ADRC controller;

[0011] S5. According to the characteristics of active output fluctuation of offshore wind farms and load disturbances in the system, an LFC model under mixed disturbances is constructed, and the ET-ADRC controller is applied to the offshore wind power flexible direct current grid-connected system.

[0012] In one embodiment of the present invention, in step S1, the LFC model of the offshore wind farm connected to the flexible direct current grid system includes an offshore wind turbine active power output model, a VSC-HVDC power transmission model, and additional inertia control.

[0013] In one embodiment of the present invention, in step S2, the multi-region system model including offshore wind power flexible direct current grid connection includes the design of an event-triggered active disturbance rejection controller.

[0014] In one embodiment of the present invention, the captured mechanical power of the offshore wind farm and the active power output equation of the offshore wind turbine are expressed as:

[0015]

[0016] Where α is the process variable calculated from the tip speed ratio and pitch angle, C P (λ,β) is the wind energy utilization coefficient, λ is the tip speed ratio, β is the pitch angle, ρ is the air density, R is the rotor radius, v is the wind speed, ω W is the fan speed, k opt is the maximum power tracking coefficient, P opt is the reference value of offshore wind turbine output power, P w is the reference value of active power output of offshore wind farm after the introduction of additional inertia control, P f is the auxiliary power of additional inertia control, k p , k d are the proportional coefficient and differential coefficient respectively, Δf is the system frequency deviation;

[0017] The VSC-HVDC power transmission model is expressed as:

[0018]

[0019] Where s is the Laplace transform operator, E vsg and D vsg The reference point P f and the disturbance ω g To output point P wv The closed-loop transfer function, P wv is the active power output of the offshore wind farm via VSC-HVDC, G vsg is the transfer function of VSC-HVDC, G g for The integral part, is the nominal angular frequency, , is the synchronous power factor, X t is the total reactance, ω g is the AC bus frequency.

[0020] In one embodiment of the present invention, the dynamic equation of the i-th (i=1, 2, 3, ..., n) sub-region containing the offshore wind farm-flexible direct current grid-connected system is expressed as:

[0021]

[0022] The dynamic system model of the entire multi-region interconnected system is expressed as:

[0023]

[0024] in, C i =[η i 1 0 0], Represents x i The derivative of (t), x i (t) is the system state, u i (t) is the control signal, ω i (t) is the disturbance, y i (t) is the output signal, A i , B i , C i 、F i is the coefficient matrix of the system state equation, ΔP mi is the change in active output of regional generators, ΔP ci is the compensation power of secondary frequency modulation, ΔP wvi is the active output change of offshore wind power-flexible direct current, ΔP Li is the load disturbance, ΔP tie,ij is the deviation of the power tie line between the two regions, Δf i is the regional frequency deviation, ACE i is the regional control deviation signal of region i, η i is the frequency deviation coefficient of a certain area of ​​the system, T pi and D i are the inertia constant and damping coefficient respectively, T Gi is the time constant of the thermal power unit speed governor, T Ti is the time constant of the thermal generator, T ij is the tie line synchronization coefficient, R i is the speed regulation factor of area i.

[0025] In one embodiment of the present invention, the sampling sequence in step S3 is:

[0026] ζ 1 ={0,T,2T,…nT,…},n∈Ν;

[0027] Wherein, T is the sampling period, and N represents a positive integer;

[0028] The continuous event triggering mechanism is expressed as:

[0029]

[0030] Among them, x(t) and x(t k ) are the current state of the system and the state at the time when the system event is triggered, e(t) is the error between the current output state of the system and the previous output state, δ is the set trigger threshold, t k is the sampling instant of the current transmission, t k+1 is the sampling instant of the next transmission;

[0031] The triggering moment is expressed as:

[0032] ζ 2 ={t 0 ,t 1 ,t 2 ,…,t k ,t k+1 ,…};

[0033] in,

[0034] In one embodiment of the present invention, after step S3, the input signal of the ET-ADRC extended state observer under the continuous event trigger mechanism is:

[0035] y i (t) = ACE i ,t∈(t k ,t k+1 );

[0036] The input signal is used to perform an expansion observation on the entire multi-region interconnected system dynamic system model in step S2 to obtain the observed state of the interconnected system, which is expressed as:

[0037]

[0038] in, is the observed state of the system; is the extended state observation obtained by the extended state observer, which is determined by the disturbance of the system. ε is used as a high gain parameter and ε is set to (0,1). g i (·) is some selected function, u(t) is the control signal, and y(t) is the output signal;

[0039] According to the observed state of the system, ET-ADRC is expressed as:

[0040]

[0041] Among them, e i (t) is defined as Here m represents the triggering time of the previous triggering event, where m represents the total number of triggering events in the time period (0, t), and δ 1 >0,k i is a constant, z(t) is the control law, and when r(t)=1, the control signal z(t) is transmitted.

[0042] In one embodiment of the present invention, step S5 includes: based on the wind speed instability faced by the offshore wind farm, constructing a mutation model of the offshore constant wind speed and an offshore random wind speed model; considering the possible conditions of the multi-region interconnected system, constructing a regional random load disturbance model, and combining the offshore random wind speed and regional random load disturbances to act on the interconnected system to construct an LFC model under mixed disturbance.

[0043] In one embodiment of the present invention, step S5 is specifically implemented as follows:

[0044] S5.1. Sudden wind at sea v a The mutation amount is the uncertain component in the model, which is used to describe the characteristics of wind speed mutation and is expressed in the mathematical model as:

[0045]

[0046] Among them, v a For sudden changes in wind at sea, T a is the mutation time;

[0047] S5.2. Random wind at sea is the main source of randomness in offshore wind power systems. The direct cause of the continuous fluctuation of the output power of offshore wind turbines is the characteristic of the continuous fluctuation of random wind speed.

[0048] To simulate random wind at sea, random noise is used to represent the randomness of wind speed changes. Therefore, filtered Gaussian white noise is selected to simulate random wind speed at sea.

[0049] The random load disturbance is expressed as a function of frequency and voltage:

[0050]

[0051] Among them, P Li is the load power, P N is the reference power, V is the voltage, V N is the voltage reference value, f is the power system frequency, f N System frequency reference value, ΔP rand is the random disturbance term, a p ,b p ,c p ,d p The parameters to be set for the model;

[0052] For the random disturbance term ΔP rand It is assumed to be a random process, and the autoregressive moving average model is used to describe its change over time, which can be expressed as:

[0053]

[0054] Among them, γ i and θ j are model parameters, p and q are model orders, and ε(t) is a white noise sequence.

[0055] The present invention also provides a computer-readable storage medium, on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0056] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides an event-triggered self-disturbance-resistance load frequency control method for an offshore wind power flexible direct current grid-connected multi-regional interconnected system in view of the fluctuation characteristics of the active power output of the offshore wind farm and the load disturbance of the multi-regional interconnected system. In addition, in order to ensure the high efficiency and stability of the system control performance, the trigger law of the ET-ADRC is proposed based on the sampling sequence of the ADRC controller and the continuous event triggering mechanism. Again, an extended state observer is designed according to the ACE signal output by the interconnected power system, and on this basis, a control law of the continuous event-triggered ADRC is designed to obtain the event-triggered ADRC load frequency controller, which is applied to the offshore wind power flexible direct current grid-connected multi-regional interconnected system. The present invention can realize the frequency stable operation of the offshore wind power flexible direct current grid-connected multi-regional interconnected system under the conditions of random changes in wind speed in the offshore wind farm and random disturbances in multi-regional loads. Finally, the effectiveness and superiority of the proposed event-triggered self-disturbance-resistance frequency control method are verified through simulation experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a schematic diagram provided by the present invention;

[0058] Figure 2 It is a schematic diagram of a model of the i-th region of a multi-region interconnected LFC system including an event-triggered active disturbance rejection control provided by the present invention;

[0059] Figure 3 This is a method for constructing a VSC-HVDC power transmission model provided by the present invention;

[0060] Figure 4 This is the control principle of a continuous event-triggered auto-disturbance rejection controller provided by the present invention;

[0061] Figure 5are the input and output values ​​of the offshore wind power grid-connected system via VSC-HVDC, Figure 5 (a) is a schematic diagram of the random wind speed model received by the offshore wind farm. Figure 5 (b) is the active power output of the offshore wind farm through VSC-HVDC under random wind speed;

[0062] Figure 6 The two-region interconnected system with offshore wind power flexible direct current grid connection provided by the example of the present invention uses the method of the present invention and the traditional method to control the frequency deviation response of the system and the active power deviation on the power tie line, wherein: Figure 6 (a) is a comparison chart of the frequency response deviation of region 1. Figure 6 (b) is the frequency response deviation comparison diagram of region 2. Figure 6 (c) is a comparison diagram of the active power deviation on the power tie line between the two regions. DETAILED DESCRIPTION

[0063] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings.

[0064] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0065] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0066] The embodiment of the present invention proposes an event-triggered self-disturbance load frequency control method for an offshore wind power flexible direct current grid-connected system to cope with unknown random load disturbances in the system, including active disturbances of offshore wind farm flexible direct current grid-connected systems. The disturbances in this embodiment refer to random fluctuations in multi-regional system loads and random fluctuations in output power of offshore wind farms affected by climate, thereby affecting the frequency deviation of the system, which may cause load shedding or even large-scale power outages in severe cases.

[0067] like Figure 1 As shown, this embodiment provides an event-triggered automatic disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system, comprising the following steps:

[0068] S1. According to the equation describing the system state of the flexible direct current transmission grid-connected system including the offshore wind farm, a LFC model of the flexible direct current grid-connected system including the offshore wind farm is constructed;

[0069] The captured mechanical power and active power output equation of the offshore wind turbine in S1 can be expressed as:

[0070]

[0071] Where α is the process variable calculated from the tip speed ratio and pitch angle, C P (λ,β) is the wind energy utilization coefficient, λ is the tip speed ratio, β is the pitch angle, ρ is the air density, R is the rotor radius, v is the wind speed, ω W is the fan speed, k opt is the maximum power tracking coefficient, P opt P is the reference value of offshore wind turbine output power. w P is the reference value of active power output of offshore wind turbine after the additional inertia control is introduced; f is the auxiliary power of additional inertia control, k p , k d are the proportional coefficient and differential coefficient respectively, Δf is the system frequency deviation;

[0072] refer to Figure 3 , the LFC model of VSC-HVDC can be expressed as:

[0073]

[0074] Where s is the Laplace transform operator, E vsg and D vsg The reference point P f and the disturbance ω g To output point P wv The closed-loop transfer function, P wv is the active power output of the offshore wind farm via VSC-HVDC, G vsg is the transfer function of VSC-HVDC, G g for The integral part, is the nominal angular frequency, , is the synchronous power factor, X t is the total reactance, ω g is the AC bus frequency, ΔP f * is the active output reference value of the virtual inertia controller, K J , K D are the proportional coefficient and differential coefficient respectively, f N is the rated frequency of the system.

[0075] S2. According to the dynamic equations of the system states expressed by each region in the interconnected system including the offshore wind farm via the flexible direct current transmission grid, a multi-region system model including the offshore wind farm flexible direct current grid connection is constructed;

[0076] See also Figure 2 As shown in Figure 2, the dynamic equation of the i-th (i=1, 2, 3, …, n) sub-area in S2 containing offshore wind power-flexible direct current grid connection can be expressed as:

[0077]

[0078] The dynamic system model of the entire multi-region interconnected system can be expressed as:

[0079]

[0080] in, C i =[η i 1 0 0], Represents x i The derivative of (t), x i (t) is the system state, u i (t) is the control signal, ω i (t) is the disturbance, y i (t) is the output signal, A i , B i , C i 、F i is the coefficient matrix of the system state equation, ΔP mi is the change in active output of regional generators, ΔP ci is the compensation power of secondary frequency modulation, ΔP wvi is the active output change of offshore wind power-flexible direct current, ΔP Li is the load disturbance, ΔP tie,ij is the deviation of the power tie line between the two regions, Δf i is the regional frequency deviation, ACE i is the regional control deviation signal of region i, η i is the frequency deviation coefficient of a certain area of ​​the system, T pi and D i are the inertia constant and damping coefficient respectively, T Gi is the time constant of the thermal power unit speed governor, T Ti is the time constant of the thermal generator, T ij is the tie line synchronization coefficient, R i is the speed regulation factor of area i;

[0081] S3. According to the sampling sequence of the ADRC controller in the multi-region interconnected power system, combined with the triggering mechanism of continuous event triggering, design the triggering condition of the continuous event triggering mechanism;

[0082] refer to Figure 4 , Figure 4 It is the continuous event triggered ADRC control principle. The control structure of the continuous event triggered ADRC controller is mainly composed of extended state observer, control law, trigger conditions and transmission network.

[0083] Assuming that the sensor is driven by a time cycle of T for sampling, the sampling sequence can be expressed as:

[0084] ζ 1 ={0,T,2T,…nT,…},n∈Ν;

[0085] Wherein, T is the adoption period, and N represents a positive integer;

[0086] The continuous event triggering mechanism can be expressed as:

[0087]

[0088] Among them, x(t) and x(t k ) are the current state of the system and the state at the time when the system event is triggered, e(t) is the error between the current output state of the system and the previous output state, δ is the set trigger threshold, t k is the sampling instant of the current transmission, t k+1 is the sampling instant of the next transmission;

[0089] The triggering moment is expressed as:

[0090] ζ 2 ={t 0 ,t 1 ,t 2 ,…,t k ,t k+1 ,…};

[0091] in,

[0092] S4. Design an extended state observer based on the ACE signal output by the interconnected power system, and on this basis, design a control law for continuous event-triggered ADRC to obtain the event-triggered ADRC controller;

[0093] In practical applications, the real-time status of the system can be evaluated through the ACE signal;

[0094] refer to Figure 4, the input signal of the ET-ADRC extended state observer under the continuous event trigger mechanism of the present invention is:

[0095] y i (t) = ACE i ,t∈(t k ,t k+1 );

[0096] The input signal is used to expand the system dynamic model in S2 to obtain the observed state of the interconnected system, which is expressed as:

[0097]

[0098] in, is the observed state of the system; is the extended state observation value obtained by the extended state observer, which is usually determined by the disturbance of the system. ε is used as a high gain parameter. In order to ensure the observation effect, ε is set to (0,1). g i (·) is some selected function, u(t) is the control signal, and y(t) is the output signal;

[0099] According to the observed state of the system, ET-ADRC can be expressed as:

[0100]

[0101] Among them, e i (t) is defined as Here m represents the triggering time of the previous triggering event, where m represents the total number of triggering events in the time period (0, t), and δ 1 >0,k i is a constant, z(t) is the control law. When r(t)=1, the control signal z(t) is transmitted.

[0102] S5. Based on the variable and unstable wind speed faced by offshore wind farms, a mutation model of offshore constant wind speed and an offshore random wind speed model are constructed; considering the possible conditions of multi-regional interconnected systems, a regional random load disturbance model is constructed, and the system model under mixed disturbance is constructed by combining the offshore random wind speed and regional random load disturbances to act on the interconnected system. This is achieved through the following steps:

[0103] S5.1. Sudden wind at sea v a The mutation amount is the uncertain component in the model, which is mainly used to describe the characteristics of wind speed mutation. It can be expressed in the mathematical model as follows:

[0104]

[0105] where v aFor sudden wind changes at sea, T a is the mutation time;

[0106] S5.2. Random wind at sea is the main source of randomness in offshore wind power systems. The direct cause of the continuous fluctuation of the output power of offshore wind turbines is the characteristic of the continuous fluctuation of random wind speed.

[0107] refer to Figure 5 (a) Random noise is usually used to simulate random wind speed changes at sea. Therefore, the present invention uses filtered Gaussian white noise to simulate random wind speed at sea;

[0108] Random load disturbances can usually be expressed as a function of frequency and voltage:

[0109]

[0110] Where P Li is the load power, P N is the reference power, V is the voltage, V N is the voltage reference value, f is the power system frequency, f N System frequency reference value, ΔP rand is the random disturbance term, a p ,b p ,c p ,d p The parameters to be set for the model;

[0111] The present invention is for the random disturbance term ΔP rand It can be assumed to be a random process, and the autoregressive moving average model is used to describe its change over time, which can be expressed as:

[0112]

[0113] Among them, γ i and θ j are model parameters, p and q are model orders, and ε(t) is a white noise sequence.

[0114] The present invention is specifically described below by an embodiment.

[0115] Based on the Matlab 2022b software platform, the present invention is used to carry out a simulation experiment of a two-region interconnected power system including offshore wind power flexible direct current grid connection, and the LFC system adopts the parameters shown in Table 1 below.

[0116] Table 1. LFC system parameters

[0117]

[0118] In Table 1, B 1 and B2 represents the frequency response coefficient of region 1 and region 2, R 1 and R 2 is the droop coefficient, T G1 and T G2 is the speed regulator time constant, T T1 and T T2 is the turbine time constant, T P1 and T P2 is the equivalent inertia coefficient, D 1 and D 2 is the equivalent damping coefficient, T 12 and T 21 is the power tie line synchronization coefficient.

[0119] In this embodiment, considering the unstable environment faced by offshore wind farms, the unstable characteristics of offshore wind power grid-connected flexible direct current are used as the disturbance of the two-region system, and the offshore random wind speed reference Figure 5 (a).

[0120] Under random wind speed, the active power output of offshore wind farms connected to the grid through VSC-HVDC can be referenced Figure 5 (b).

[0121] In this embodiment, the two-region model uses the ET-ADRC controller of the present invention and the traditional PI control for comparative experiments. Both regions of the experimental group use the ET-ADRC control method of the present invention, while the control group uses the traditional PI controller.

[0122] At the beginning of the simulation, the active power output of the above offshore wind power through VSC-HVDC is injected into region 1 of the two-region LFC system as a disturbance. The frequency response deviation of the system and the deviation of the power tie line are as follows: Figure 6 shown.

[0123] Depend on Figure 6 (a)-(c) show that, when the two-region power system is injected with offshore wind power via flexible direct current grid connection as disturbance, both the experimental group and the control group can effectively suppress the frequency fluctuation of the system. However, compared with the traditional PI controller, under the ET-ADRC control method described in the present invention, the fluctuation amplitude of each system deviation is smaller, the overshoot is lower, and the convergence speed is faster, so that the two-region system has better stability and anti-interference ability.

[0124] The integral time square error (ITSE) is introduced. The smaller the value of the ITSE, the better the system performance and the better the control effect. By calculating the ITSE of the two-region system, the control effects of ET-ADRC and traditional PI can be more clearly compared. The comparison between the experimental group and the control group is shown in Table 2, where the experimental group and the control group are LFC systems with offshore wind power connected to the grid using ET-ADRC controller and ET-PI controller, respectively.

[0125] The ITSE calculation method can be expressed as:

[0126]

[0127] Among them, T max is the simulation running time.

[0128] Table 2. TESE performance indicators of the two-region interconnected system when the offshore wind power flexible direct current grid-connected system is disturbed

[0129] Control Methods ET-PI ET-ADRC ITSE 1.8 0.073

[0130] By comparing the ITSE of the experimental group and the control group, it can be determined that the ET-ADRC control method described in the present invention can more quickly and accurately control the deviations of the power systems in the two regions to near the standard values, thereby making the system have a more ideal dynamic response performance.

[0131] In summary, the present invention designs the ET-ADRC control method for the uncertainty of the output power of offshore wind farms (including unknown random load disturbances), and combines event-triggered control and ADRC methods to achieve effective control of the frequency fluctuations of the new power system containing offshore wind power flexible direct current grid connection, so that the LFC system has a more ideal dynamic response performance. At the same time, additional inertia control is used to effectively suppress the output fluctuations of offshore wind power and VSC-HVDC. It should be noted that the method of the present invention not only plays a role in the disturbance of offshore wind power flexible direct current grid connection, but can also be used to regulate the fluctuations generated by multi-regional interconnected power systems under any random load disturbances.

[0132] The present invention also provides a computer-readable storage medium, on which computer program instructions that can be executed by a processor are stored. When the processor executes the computer program instructions, the method steps described above can be implemented.

[0133] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0134] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0135] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0136] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0137] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. An event-triggered auto-disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system, characterized in that: include: S1. Construct the LFC model of the offshore wind farm connected to the grid via flexible direct current; S2. Based on the dynamic equations of the system states expressed by each region in the interconnected system including offshore wind farms connected to the grid via flexible direct current transmission, a multi-region system model including offshore wind farms connected to the grid via flexible direct current transmission is constructed; S3. Design the triggering conditions of the continuous event triggering mechanism based on the sampling sequence of the ADRC controller in the multi-region interconnected power system and the continuous event triggering mechanism; S4. Design an extended state observer based on the ACE signal output by the interconnected power system, and on this basis, design a control law for continuous event-triggered ADRC to obtain an event-triggered ADRC controller, namely, an ET-ADRC controller; S5. According to the characteristics of active output fluctuation of offshore wind farms and load disturbances in the system, an LFC model under mixed disturbances is constructed, and the ET-ADRC controller is applied to the offshore wind power flexible direct current grid-connected system.

2. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 1, characterized in that: In step S1, the LFC model of the offshore wind farm connected to the flexible direct current grid system includes an offshore wind turbine active power output model, a VSC-HVDC power transmission model, and additional inertia control.

3. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 1, characterized in that: In step S2, the multi-region system model including offshore wind power flexible direct current grid connection includes the design of an event-triggered active disturbance rejection controller.

4. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 2, characterized in that: The captured mechanical power of the offshore wind farm and the active output equation of the offshore wind turbine are expressed as: Where α is the process variable calculated from the tip speed ratio and pitch angle, C P (λ,β) is the wind energy utilization coefficient, λ is the tip speed ratio, β is the pitch angle, ρ is the air density, R is the rotor radius, v is the wind speed, ω W is the fan speed, k opt is the maximum power tracking coefficient, P opt is the reference value of offshore wind turbine output power, P w is the reference value of active power output of offshore wind farm after the introduction of additional inertia control, P f is the auxiliary power of additional inertia control, k p , k d are the proportional coefficient and differential coefficient respectively, Δf is the system frequency deviation; The VSC-HVDC power transmission model is expressed as: Where s is the Laplace transform operator, E vsg and D vsg The reference point P f and the disturbance ω g To output point P wv The closed-loop transfer function, P wv is the active power output of the offshore wind farm via VSC-HVDC, G vsg is the transfer function of VSC-HVDC, G g for The integral part, is the nominal angular frequency, is the synchronous power factor, X t is the total reactance, ω g is the AC bus frequency.

5. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 4, characterized in that: The dynamic equation of the i-th (i=1, 2, 3, …, n) sub-region containing the offshore wind farm-flexible direct current grid-connected system is expressed as: The dynamic system model of the entire multi-region interconnected system is expressed as: in, C i =[η i 1 0 0], Represents x i The derivative of (t), x i (t) is the system state, u i (t) is the control signal, ω i (t) is the disturbance, y i (t) is the output signal, A i , B i , C i 、F i is the coefficient matrix of the system state equation, ΔP mi is the change in active output of regional generators, ΔP ci is the compensation power of secondary frequency modulation, ΔP wvi is the active output change of offshore wind power-flexible direct current, ΔP Li is the load disturbance, ΔP tie,ij is the deviation of the power tie line between the two regions, Δf i is the regional frequency deviation, ACE i is the regional control deviation signal of region i, η i is the frequency deviation coefficient of a certain area of ​​the system, T pi and D i are the inertia constant and damping coefficient respectively, T Gi is the time constant of the thermal power unit speed governor, T Ti is the time constant of the thermal generator, T ij is the tie line synchronization coefficient, R i is the speed regulation factor of area i.

6. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 5, characterized in that: The sampling sequence in step S3 is: ζ1={0,T,2T,nT,…},n∈Ν; Wherein, T is the sampling period, and N represents a positive integer; The continuous event triggering mechanism is expressed as: Among them, x(t) and x(t k ) are the current state of the system and the state at the time when the system event is triggered, e(t) is the error between the current output state of the system and the previous output state, δ is the set trigger threshold, t k is the sampling instant of the current transmission, t k+1 is the sampling instant of the next transmission; The triggering moment is expressed as: ζ2={t0,t1,t2,…,t k ,t k+1 ,…}; in, 7. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 6, characterized in that: After step S3, the input signal of the ET-ADRC extended state observer under the continuous event trigger mechanism is: y i (t)=ACE i ,t∈(t k ,t k+1 ); The input signal is used to perform an expansion observation on the entire multi-region interconnected system dynamic system model in step S2 to obtain the observed state of the interconnected system, which is expressed as: in, is the observed state of the system; is the extended state observation obtained by the extended state observer, which is determined by the disturbance of the system. ε is used as a high gain parameter and ε is set to (0,1). g i (·) is the selected function, u(t) is the control signal, and y(t) is the output signal; According to the observed state of the system, ET-ADRC is expressed as: Among them, e i (t) is defined as Here m Indicates the triggering time of the previous triggering event, where m represents the total number of triggering events in the time period (0, t), δ1>0, k i is a constant, z(t) is the control law, and when r(t)=1, the control signal z(t) is transmitted.

8. The event-triggered auto-disturbance rejection frequency control method for an offshore wind power flexible direct current grid-connected system according to claim 7, characterized in that: Step S5 includes: based on the wind speed instability faced by offshore wind farms, constructing a mutation model of offshore constant wind speed and an offshore random wind speed model; considering the possible conditions of multi-regional interconnected systems, constructing a regional random load disturbance model, and combining the offshore random wind speed and regional random load disturbances to act on the interconnected system to construct an LFC model under mixed disturbances.

9. The event-triggered auto-disturbance rejection frequency control method of an offshore wind power flexible direct current grid-connected system according to claim 7 or 8, characterized in that: Step S5 is specifically implemented as follows: S5.

1. Sudden wind at sea v a The mutation amount is the uncertain component in the model, which is used to describe the characteristics of wind speed mutation and is expressed in the mathematical model as: Among them, v a For sudden changes in wind at sea, T a is the mutation time; S5.

2. Random wind at sea is the main source of randomness in offshore wind power systems. The direct cause of the continuous fluctuation of the output power of offshore wind turbines is the characteristic of the continuous fluctuation of random wind speed. To simulate random wind at sea, random noise is used to represent the randomness of wind speed changes. Therefore, filtered Gaussian white noise is selected to simulate random wind speed at sea. The random load disturbance is expressed as a function of frequency and voltage: Among them, P Li is the load power, P N is the reference power, V is the voltage, V N is the voltage reference value, f is the power system frequency, f N System frequency reference value, ΔP rand is the random disturbance term, a p ,b p ,c p ,d p The parameters to be set for the model; For the random disturbance term ΔP rand It is assumed to be a random process, and the autoregressive moving average model is used to describe its change over time, which can be expressed as: Among them, γ i and θ j are model parameters, p and q are model orders, and ε(t) is a white noise sequence.

10. A computer-readable storage medium having stored thereon computer program instructions that can be executed by a processor, and when the processor executes the computer program instructions, the method steps according to any one of claims 1 to 9 can be implemented.

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