Non-linear control method and device for network-building converter based on feedback linearization

Abstract

The invention discloses a feedback linearization-based non-linear control method and device for a network construction type converter. The method comprises the following steps: simplifying a network-forming converter in a grid-connected system into a constant voltage source, simulating a rotor motion equation and excitation regulation characteristics of a synchronous machine, and determining a control system model of the grid-connected system where the network-forming converter is located; converting the determined control system model of the grid-connected system where the grid-forming converter is located into a state space model; constructing a differential homeomorphism for the two-input and two-output affine nonlinear system; mapping the two-input and two-output affine nonlinear system into a linearization system by using the constructed differential homeomorphism; an output feedback linearization controller is constructed at the front end of the constructed differential homeomorphism, and a mapped linearization system is converted into an output feedback linearization network construction type converter grid-connected control system model; the designed control parameters and the constructed output feedback linearization controller are used for controlling the network-forming converter, the control precision is high, and the system is more stable.

Description

Technical Field

[0001] This invention belongs to the technical field of grid converters, specifically relating to a nonlinear control method and device for grid converters based on feedback linearization. Background Technology

[0002] Grid-Forming Converters, based on grid-formed control, can provide a certain amount of inertia and damping support for the power grid. They have certain application prospects and value in weak power grid scenarios with large-scale new energy access and have become a research hotspot in the field of new energy grid connection.

[0003] To reduce the coupling between active and reactive power control links in grid-type control systems, various decoupling control methods exist. However, these methods either fail to eliminate the coupling between active and reactive power, resulting in some control error, or may reduce the stability margin of the grid-type converter, leading to system oscillations.

[0004] Therefore, it is necessary to propose control methods that can improve the control accuracy of grid-type converters and / or maintain system stability. Summary of the Invention

[0005] In view of this, the present invention provides a nonlinear control method and apparatus for grid-type converters based on feedback linearization, aiming to solve the technical problems of insufficient control accuracy or insufficient system stability of grid-type converters in the prior art.

[0006] In a first aspect, the present invention provides a nonlinear control method for a network converter based on feedback linearization, comprising:

[0007] The grid-connected converter in the grid-connected system is simplified as a constant voltage source, and the rotor motion equation and excitation regulation characteristics of the synchronous machine are simulated to determine the control system model of the grid-connected system where the grid-connected converter is located.

[0008] The control system model of the grid-connected system where the grid-connected converter is located is converted into a state-space model. The converted state-space model is an affine nonlinear system with two inputs and two outputs.

[0009] A differential homeomorphism is constructed for the two-input, two-output affine nonlinear system; the constructed differential homeomorphism is used to map the two-input, two-output affine nonlinear system into a linearized system;

[0010] An output feedback linearization controller is constructed at the front end of the constructed differential homeomorphism, and the mapped linearized system is transformed into an output feedback linearized grid-connected converter control system model.

[0011] The control parameters of the constructed output feedback linearization controller are designed, and the grid-type converter is controlled using the designed control parameters and the constructed output feedback linearization controller.

[0012] Furthermore, the process of simplifying the grid-connected converter in the grid-connected system as a constant voltage source and simulating the rotor motion equation and excitation regulation characteristics of a synchronous machine to determine the control system model of the grid-connected system where the grid-connected converter is located includes:

[0013] The grid-connected converter in the grid-connected system is simplified as a constant voltage source, where E is the equivalent internal potential of the grid-connected converter;

[0014] The rotor motion equations and excitation regulation characteristics of the grid-type converter simulating a synchronous machine are controlled. The outer loop controller for the grid-type converter includes an active-frequency control branch and a reactive-voltage control branch. The active-frequency control branch is based on the acquired active power reference value P0, angular frequency reference value ω0, dynamic active power P, dynamic angular frequency ω, and first damping coefficient D. p The first feedforward coefficient J maintains system frequency stability; the reactive power-voltage control branch uses the acquired voltage reference value V0, reactive power reference value Q0, dynamic reactive power Q, equivalent internal potential E of the grid-type converter, and second damping coefficient D. q And the second feedforward coefficient K maintains voltage stability;

[0015] The control system model of the grid-connected system in which the grid-connected converter is located is shown in the following equation:

[0016]

[0017] Where E0 is the rated equivalent internal potential of the grid-type converter; δ is the power angle; V g X is the equivalent voltage of the power grid. s This refers to the internal impedance of a grid-type converter.

[0018] Furthermore, the conversion of the control system model of the grid-connected system where the determined grid-connected converter is located into a state-space model includes:

[0019] The grid angular frequency ω, the equivalent internal electromotive force E of the grid-type converter, and the power angle δ are determined as state variables x1, x2, and x3, respectively, forming the state vector x; the reciprocals of the first feedforward coefficient J and the second feedforward coefficient K are determined as control input variables u1 and u2, respectively, forming the control input vector u; the equivalent internal electromotive force E and the power angle δ of the grid-type converter are determined as output variables y1 and y2, respectively, forming the output vector y, as shown in the following equation, where T represents the transpose operation:

[0020]

[0021] The control system model of the grid-connected system containing the grid-type converter is converted into a state-space model using the state vector, the control input vector, and the output vector, as shown in the following equation:

[0022]

[0023] The first state variable function matrix f(x) is shown in the following equation:

[0024]

[0025] The first control input function vector g1(x) and the second control input function vector g2(x) are shown in the following equations:

[0026]

[0027] The first output function vector h1(x) and the second output function vector h2(x) are shown in the following equations:

[0028]

[0029] Wherein, the inherent parameter of the first system is a = 3V g / X s The second system's inherent parameter b = 3 / X s The third system's inherent parameter c = D p / ω0;The fourth system's intrinsic parameter d=P0 / ω0+D p The fifth system's inherent parameter e = D q The sixth system's inherent parameter f = Q0 + E0D q .

[0030] Further, the construction of a differential homeomorphism for the two-input, two-output affine nonlinear system; and the mapping of the two-input, two-output affine nonlinear system to a linearized system using the constructed differential homeomorphism, includes:

[0031] The first-order derivatives of the output variables of the affine nonlinear system are defined as the input vectors of the diffeomorphism, denoted as...

[0032] The output vector of the differential homeomorphism is determined to be the control input vector of the affine nonlinear system.

[0033] The state variable of the differential homeomorphism is determined to be the state variable x of the affine nonlinear system;

[0034] The expression for determining the differential homeomorphism is shown below:

[0035]

[0036] The second state variable function matrix E(x) is shown in the following equation:

[0037]

[0038] Third state variable function matrix A -1 (x) is shown in the following formula:

[0039]

[0040] The constructed differential homeomorphism is placed at the front end of the affine nonlinear system, and the two-input, two-output affine nonlinear system is mapped to a linearized system, so that the constructed differential homeomorphism and the affine nonlinear system together constitute a linearized grid-connected converter control system model.

[0041] Furthermore, the step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism, and converting the mapped linearized system into an output feedback linearized grid-connected converter control system model, includes:

[0042] For the grid-connected control system model of a linearized grid-connected converter, an output feedback linearized controller is constructed; wherein, the output variable of the output feedback linearized controller is the input variable of the differential homeomorphism, and the output variable of the affine nonlinear system is fed back to the control input terminal of the output feedback linearized controller;

[0043] The output feedback linearization controller includes an equivalent internal potential linearization control branch and a power angle linearization control branch.

[0044] Furthermore, the step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism includes:

[0045] The constructed output feedback linearization controller is shown in the following equation:

[0046]

[0047] Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij These are the constant coefficients of each element within the linearization controller, where i is 1 or 2, and j is 1 or 2.

[0048] Furthermore, the step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism includes:

[0049] The constructed output feedback linearization controller is shown in the following equation:

[0050]

[0051] Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij These are the constant coefficients of each element within the linearization controller, where i is 1 or 2, and j is 1, 2, or 3.

[0052] Secondly, the present invention provides a nonlinear control device for a grid-type converter based on feedback linearization, comprising:

[0053] The control system model determination unit is used to simplify the grid-connected converter in the grid-connected system into a constant voltage source and simulate the rotor motion equation and excitation regulation characteristics of the synchronous machine, thereby determining the control system model of the grid-connected system in which the grid-connected converter is located.

[0054] The state-space model determination unit is used to convert the control system model of the grid-connected system where the grid-connected converter is located into a state-space model. The converted state-space model is an affine nonlinear system with two inputs and two outputs.

[0055] A linearized system mapping unit is used to construct a differential homeomorphism for the two-input, two-output affine nonlinear system; and to map the two-input, two-output affine nonlinear system into a linearized system using the constructed differential homeomorphism.

[0056] The output feedback linearization controller construction unit is used to construct an output feedback linearization controller at the front end of the constructed differential homeomorphism, and to convert the mapped linearized system into an output feedback linearization grid-connected converter control system model.

[0057] The grid-type converter control unit is used to design the control parameters of the constructed output feedback linearization controller; the designed control parameters and the constructed output feedback linearization controller are used to control the grid-type converter.

[0058] Thirdly, the present invention provides a terminal comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, the processor executing the computer program to implement the method described in the first aspect.

[0059] Fourthly, the present invention provides a computer storage medium storing computer-executable instructions for performing the method described in the first aspect.

[0060] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0061] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0062] Figure 1 This is a flowchart illustrating the nonlinear control method for a network converter based on feedback linearization according to an embodiment of the present invention.

[0063] Figure 2 This is a simplified grid-connected schematic diagram of a grid-type converter in the nonlinear control method for grid-type converters based on feedback linearization according to an embodiment of the present invention.

[0064] Figure 3 This is a schematic diagram of grid-connected grid converter in the nonlinear control method for grid-connected grid converter based on feedback linearization according to an embodiment of the present invention.

[0065] Figure 4 This is a block diagram of the Pf control in the nonlinear control method for a grid-type converter based on feedback linearization according to an embodiment of the present invention.

[0066] Figure 5 This is a block diagram of the QV control in the nonlinear control method for a grid-type converter based on feedback linearization according to an embodiment of the present invention.

[0067] Figure 6 This is a schematic diagram of active and reactive power coupling in the nonlinear control method for a grid-type converter based on feedback linearization according to an embodiment of the present invention.

[0068] Figure 7 This is a simplified structural diagram of the network control in the nonlinear control method for network converters based on feedback linearization according to an embodiment of the present invention.

[0069] Figure 8 This is a simplified diagram of the differential homeomorphism construction and feedback linearization controller structure in the nonlinear control method for a network converter based on feedback linearization according to an embodiment of the present invention.

[0070] Figure 9 The above is a comparison of simulation results of the nonlinear control method for a network converter based on feedback linearization according to an embodiment of the present invention in various scenarios.

[0071] Figure 10 This is a schematic diagram of the composition of a nonlinear control device for a grid-type converter based on feedback linearization according to an embodiment of the present invention;

[0072] Figure 11 A schematic diagram of the terminal for applying the feedback linearization-based nonlinear control method for a grid-type converter according to an embodiment of the present invention;

[0073] Figure 12 A schematic diagram of a computer storage medium for applying the feedback linearization-based nonlinear control method for a grid-type converter according to an embodiment of the present invention. Detailed Implementation

[0074] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are illustrated in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, the embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0075] Grid-type converters can generate stable AC voltage waveforms on their own. Specifically, they internally set or generate reference voltage amplitude, frequency, and phase angle or power angle according to a control strategy, and control their output voltage to strictly follow this internal reference. When connected to a load or other power source, similar to a synchronous generator maintaining system frequency and voltage by adjusting rotor speed and excitation, the grid-type converter automatically adjusts its output voltage and current to maintain its set voltage and frequency. However, there is coupling between the active power control and reactive power control links in grid-type converters.

[0076] To reduce the coupling between active and reactive power control links in a grid-type control system, the transfer function method considers the multi-time-scale control effects of active and reactive power control and inner-loop control, constructs the transfer function of the overall control link of the grid-type converter, derives the mapping relationship between the parameters of the grid-type control link and the coupling components, and reduces the coupling by adjusting the control parameters. However, this strategy cannot completely eliminate the coupling between active and reactive power, and a certain amount of control error still exists.

[0077] To reduce the coupling between active and reactive power control loops in grid-type control systems, the virtual impedance method interprets this coupling from the perspective of the control loops, assuming an impedance correlation between the two control loops. This strategy simulates a virtual impedance in the inner loop control that has the same magnitude but opposite sign as the coupling impedance, thereby canceling the coupling relationship between the active and reactive power control loops. However, the introduction of virtual impedance will cause changes in the impedance characteristics of the grid-type converter, potentially reducing its stability margin and causing system oscillations, such as frequency and voltage instability.

[0078] Furthermore, the coupling between active and reactive power control components also complicates parameter tuning. Inappropriate control parameters will introduce non-negligible control errors. These errors may cause power imbalances within the system, leading to a reduction in system stability margin.

[0079] To address the frequency and voltage instability issues caused by active and reactive power coupling in grid-connected converters, this invention proposes a technical solution for nonlinear control of grid-connected converters based on feedback linearization. This solution includes a nonlinear control method and apparatus for grid-connected converters based on feedback linearization. While preserving the nonlinear characteristics of the grid-connected converter, it utilizes differential homeomorphism to construct a feedback linearization controller, which can generate stable AC voltage waveforms and improve the grid-connected stability of the grid-connected converter.

[0080] like Figure 1 As shown, the present invention provides a nonlinear control method for a grid-type converter based on feedback linearization, including the following steps S100, S200, S300, S400 and S500.

[0081] S100: Simplify the grid-connected converter in the grid-connected system into a constant voltage source and simulate the rotor motion equation and excitation regulation characteristics of the synchronous machine to determine the control system model of the grid-connected system where the grid-connected converter is located.

[0082] S200: Convert the control system model of the grid-connected system where the grid-connected converter is located into a state-space model. The converted state-space model is an affine nonlinear system with two inputs and two outputs.

[0083] S300: Construct a differential homeomorphism for the two-input, two-output affine nonlinear system; use the constructed differential homeomorphism to map the two-input, two-output affine nonlinear system into a linearized system;

[0084] S400: Construct an output feedback linearization controller at the front end of the constructed differential homeomorphism, and convert the mapped linearized system into an output feedback linearized grid-connected converter grid control system model;

[0085] S500: Design the control parameters of the constructed output feedback linearization controller, and use the designed control parameters and the constructed output feedback linearization controller to control the grid-type converter.

[0086] In some embodiments, step S100, which involves simplifying the grid-connected converter in the grid-connected system as a constant voltage source and simulating the rotor motion equation and excitation regulation characteristics of a synchronous machine to determine the control system model of the grid-connected system where the grid-connected converter is located, includes:

[0087] The grid-connected converter in the grid-connected system is simplified as a constant voltage source, where E is the equivalent internal potential of the grid-connected converter;

[0088] The rotor motion equations and excitation regulation characteristics of the grid-type converter simulating a synchronous machine are controlled. The outer loop controller for the grid-type converter includes an active-frequency control branch and a reactive-voltage control branch. The active-frequency control branch is based on the acquired active power reference value P0, angular frequency reference value ω0, dynamic active power P, dynamic angular frequency ω, and first damping coefficient D. p The first feedforward coefficient J maintains system frequency stability; the reactive power-voltage control branch uses the acquired voltage reference value V0, reactive power reference value Q0, dynamic reactive power Q, equivalent internal potential E of the grid-type converter, and second damping coefficient D. q And the second feedforward coefficient K maintains voltage stability;

[0089] The control system model of the grid-connected system in which the grid-connected converter is located is shown in the following equation:

[0090]

[0091] Where E0 is the rated equivalent internal potential of the grid-type converter; δ is the power angle; V g X is the equivalent voltage of the power grid. s This refers to the internal impedance of a grid-type converter.

[0092] In some embodiments, step S200, converting the control system model of the grid-connected system where the determined grid-connected converter is located into a state-space model, includes:

[0093] The grid angular frequency ω, the equivalent internal electromotive force E of the grid-type converter, and the power angle δ are determined as state variables x1, x2, and x3, respectively, forming the state vector x; the reciprocals of the first feedforward coefficient J and the second feedforward coefficient K are determined as control input variables u1 and u2, respectively, forming the control input vector u; the equivalent internal electromotive force E and the power angle δ of the grid-type converter are determined as output variables y1 and y2, respectively, forming the output vector y, as shown in the following equation, where T represents the transpose operation:

[0094]

[0095] The control system model of the grid-connected system containing the grid-type converter is converted into a state-space model using the state vector, the control input vector, and the output vector, as shown in the following equation:

[0096]

[0097] The first state variable function matrix f(x) is shown in the following equation:

[0098]

[0099] The first control input function vector g1(x) and the second control input function vector g2(x) are shown in the following equations:

[0100]

[0101] The first output function vector h1(x) and the second output function vector h2(x) are shown in the following equations:

[0102]

[0103] Wherein, the inherent parameter of the first system is a = 3V g / X s The second system's inherent parameter b = 3 / X s The third system's inherent parameter c = D p / ω0;The fourth system's intrinsic parameter d=P0 / ω0+D p The fifth system's inherent parameter e = D q The sixth system's inherent parameter f = Q0 + E0D q .

[0104] In some embodiments, step S300, which involves constructing a differential homeomorphism for the two-input, two-output affine nonlinear system and mapping the two-input, two-output affine nonlinear system to a linearized system using the constructed differential homeomorphism, includes:

[0105] The first-order derivatives of the output variables of the affine nonlinear system are defined as the input vectors of the diffeomorphism, denoted as...

[0106] The output vector of the differential homeomorphism is determined to be the control input vector of the affine nonlinear system.

[0107] The state variable of the differential homeomorphism is determined to be the state variable x of the affine nonlinear system;

[0108] The expression for determining the differential homeomorphism is shown below:

[0109]

[0110] The second state variable function matrix E(x) is shown in the following equation:

[0111]

[0112] Third state variable function matrix A -1 (x) is shown in the following formula:

[0113]

[0114] The constructed differential homeomorphism is placed at the front end of the affine nonlinear system, and the two-input, two-output affine nonlinear system is mapped to a linearized system, so that the constructed differential homeomorphism and the affine nonlinear system together constitute a linearized grid-connected converter control system model.

[0115] In some embodiments, step S400, which involves constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism to convert the mapped linearized system into an output feedback linearized grid-connected converter control system model, includes:

[0116] For the grid-connected control system model of a linearized grid-connected converter, an output feedback linearized controller is constructed; wherein, the output variable of the output feedback linearized controller is the input variable of the differential homeomorphism, and the output variable of the affine nonlinear system is fed back to the control input terminal of the output feedback linearized controller;

[0117] The output feedback linearization controller includes an equivalent internal potential linearization control branch and a power angle linearization control branch.

[0118] In some embodiments, step S400, which involves constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism, includes:

[0119] The constructed output feedback linearization controller is shown in the following equation:

[0120]

[0121] Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij The constant coefficients of each component within the linearized controller are i and j, respectively, where i is 1 or 2 and j is 1 or 2. The power angle linearization control branch acquires the internal potential control error and generates a control quantity as the input variable of the differential homeomorphism. The control quantity and the internal potential control error satisfy the linearized controller G... e (s); The power angle linearization control branch acquires the power angle control error and generates a control quantity as the input variable of the differential homeomorphism, wherein the control quantity and the power angle control error satisfy the linearization controller G. d (s).

[0122] In some embodiments, step S400, which involves constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism, includes:

[0123] The constructed output feedback linearization controller is shown in the following equation:

[0124]

[0125] Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij The constant coefficients of each component within the linearized controller are given, where i is 1 or 2, and j is 1, 2, or 3. The power angle linearization control branch acquires the internal potential control error and generates a control quantity as the input variable of the differential homeomorphism. The control quantity and the internal potential control error satisfy the linearized controller G... e (s); The power angle linearization control branch acquires the power angle control error and generates a control quantity as the input variable of the differential homeomorphism, wherein the control quantity and the power angle control error satisfy the linearization controller G. d (s).

[0126] The following combination Figures 2 to 9 This invention provides a detailed description of the nonlinear control method for a network converter based on feedback linearization in embodiments of the present invention.

[0127] Step S10: Obtain the control system model of the grid-connected system where the grid-connected converter is located. The control system model of the grid-connected system where the grid-connected converter is located is a nonlinear system.

[0128] like Figure 2 The simplified grid-connected diagram of a grid-connected converter shows that the grid-connected converter autonomously constructs its voltage, exhibiting voltage source characteristics. In a grid-connected system, it is simplified as a constant voltage source. In the diagram, E is the equivalent internal potential of the grid-connected converter, and X... s X is the internal impedance of the grid-type converter. g V is the power grid impedance. g V is the equivalent voltage of the power grid. s This refers to the voltage at the point of common coupling (PCC).

[0129] like Figure 3 The grid-connected schematic diagram of the grid-connected converter shows that the grid-connected converter uses a dq coordinate system to simulate the rotor motion equation and excitation regulation characteristics of a synchronous machine, tracking ω (i.e., δ) in real time to ensure synchronization between the equipment and the grid. Its outer loop controller includes an active-frequency (Pf) control branch and a reactive-voltage (QV) control branch. The active-frequency control branch is used to maintain frequency stability, and the reactive-voltage control branch is used to maintain voltage stability. This should be understood as... Figure 3 The variables shown have meanings known in the field and will not be elaborated further.

[0130] like Figure 4As shown in the Pf control block diagram, the inputs or outputs of the active-frequency (Pf) control branch include: active reference value P0, angular frequency reference value ω0, dynamic active power P, dynamic angular frequency ω, and damping coefficient D of the Pf control branch. p , Pf control branch feedforward coefficient J.

[0131] like Figure 5 As shown in the QV control block diagram, the inputs or outputs of the reactive-voltage (QV) control branch include: voltage reference value V0, reactive power reference value Q0, dynamic reactive power Q, equivalent internal potential E of the grid-type converter, and damping coefficient D of the QV control branch. q , Pf control branch feedforward coefficient K.

[0132] like Figure 3 The schematic diagram of a grid-connected converter is shown. The control of the grid-connected converter simulates the rotor motion equations and excitation regulation characteristics of a synchronous machine. Its inner loop controller includes a voltage loop and a current loop. Figure 4 , Figure 5 Replace to Figure 3 The corresponding parts, after being organized, are as follows: Figure 6 The control block diagram shown.

[0133] Specifically, such as Figure 3 and Figure 6 As shown, the control system model of the grid-connected system where the grid-connected converter is located, or the control loop expression or control system equation of the grid-connected converter, is shown in equation (1):

[0134]

[0135] In equation (1), ω is the grid angular frequency, ω0 is the reference value of the angular frequency; E is the equivalent internal potential of the grid-type converter, E0 is the rated equivalent internal potential of the grid-type converter; δ is the power angle, which can be obtained by integrating with respect to the angular frequency; D q D is the damping coefficient of the QV control branch; p The damping coefficient of the Pf control branch; J and K are the feedforward coefficients of the QV control branch and the Pf control branch, respectively; P0 is the active power reference value, and Q0 is the reactive power reference value; V g X is the equivalent voltage of the power grid. s This refers to the internal impedance of a grid-type converter.

[0136] The differential equation system of equation (1) contains nonlinear terms, and the control link of the grid-type converter has a nonlinear relationship. The control system model of the grid-connected system where the grid-type converter is located is a typical nonlinear system.

[0137] like Figure 3 and Figure 6As shown, due to the existence of inner-loop control, there is coupling between the active and reactive power control links in the grid-type control. This coupling relationship leads to insufficient precision in the frequency control and voltage control of the grid-type control, which in turn causes a decrease in system stability and triggers system oscillation.

[0138] S20: Convert the control system model of the grid-connected system where the grid-connected converter is located into state-space equations; wherein, the converted state-space model is an affine nonlinear system with two inputs and two outputs.

[0139] Specifically, the grid angular frequency ω, the equivalent internal electromotive force E of the grid-type converter, and the power angle δ are determined to be state variables x1, x2, and x3 respectively, forming a state vector. The state vector x is a 3-element vector with x1, x2, and x3. The reciprocals of the first feedforward coefficient J and the second feedforward coefficient K are determined to be the reciprocals of the feedforward coefficients J and K of the Pf branch and the QV branch respectively, forming control input variables u1 and u2 respectively, forming a control input vector u. The control input vector u is a 2-element vector with u1 and u2. The equivalent internal electromotive force E and the power angle δ of the grid-type converter are determined to be output variables y1 and y2 respectively, forming an output vector y. The output vector y is a 2-element vector with y1 and y2, as shown in equation (2), where T is the transpose operation:

[0140]

[0141] By using the state vector, control input vector, and output vector to transform the differential equations shown in equation (1), a control system model in state-space form is obtained. The control system model includes the first-order differential form control equations and output equations shown in equation (3).

[0142] The first-order differential form of the control equation and the output equation (3) are shown below:

[0143]

[0144] The first state variable function matrix f(x) is shown in equation (4):

[0145]

[0146] The first control input function vector g1(x) and the second control input function vector g2(x) are shown in equation (5):

[0147]

[0148] The first output function vector h1(x) and the second output function vector h2(x) are shown in equation (6):

[0149]

[0150] In equation (4), the inherent parameter of the first system is a = 3V g / X s The second system's inherent parameter b = 3 / X s ;

[0151] In equation (5), the inherent parameter of the third system is c = D p / ω0;The fourth system's intrinsic parameter d=P0 / ω0+D p The fifth system's inherent parameter e = D q The sixth system's inherent parameter f = Q0 + E0D q .

[0152] Thus, the control system equations in equation (1) are transformed into a control system model represented by equations (2), (3), (4), (5) and (6).

[0153] The above control system model represents the typical mathematical equations of a two-input, two-output affine nonlinear system. The corresponding typical structure of a two-input, two-output affine nonlinear system is as follows: Figure 7 As shown, the two inputs are the aforementioned control inputs u1 and u2, which are the reciprocals of the feedforward coefficients J and K of the Pf branch and QV branch, respectively; the two output variables are the aforementioned output variables y1 and y2, which are the equivalent internal electromotive force E and power angle δ of the grid-type converter; the state variables are the aforementioned x1, x2 and x3, which are the grid angular frequency ω, the equivalent internal electromotive force E of the grid-type converter, and the power angle δ.

[0154] S30: Linearize the nonlinear system for more precise control.

[0155] Specifically, a differential homeomorphism is constructed, and the control system model or affine nonlinear system of the grid-connected system where the grid-type converter is located is mapped to a linearized system using the constructed differential homeomorphism, which also realizes the linearization of the transformed state-space equations.

[0156] Constructing a differential homeomorphism includes: such as Figure 8 As shown, the first-order differentials of the output variables of the affine nonlinear system shown in equation (2) are determined as the input vectors of the diffeomorphism, denoted as . The output vector of the differential homeomorphism is determined as follows: That is, the control input vector of the affine nonlinear system; the state variables of the differential homeomorphism are determined as follows. The expression for determining the homeomorphism is shown in equation (9):

[0157]

[0158] The second state variable function matrix is ​​shown in equation (8), and the third state variable function matrix is ​​shown in equation (9).

[0159]

[0160] Specifically, the first-order differentials of the output variables of the affine nonlinear system are defined as the input vectors of the diffeomorphism, denoted as... Specifically, it includes:

[0161] Take the first derivative or perform the first differential on the output vector y in equation (2) or equation (3), such as letting Figure 8 The leftmost example shows the difference form: That is, output feedback.

[0162] Towards Figure 7 The differential homeomorphism is added to the converter grid-connected system shown.

[0163] Specifically, the constructed differential homeomorphism is placed at the front end of the affine nonlinear system, and the constructed differential homeomorphism and the affine nonlinear system together constitute a linearized grid-connected converter control system model. Thus, using the constructed differential homeomorphism, the nonlinear grid-connected converter system can be transformed from nonlinear to linear characteristics.

[0164] Specifically, before constructing the differential homeomorphism, it also includes: for equations (2) to (6), determining that the nonlinear system satisfies the Frobenius theorem and can be precisely linearized.

[0165] S40: For the grid-connected control system model of the output feedback linearized grid-type converter obtained by mapping, a linearized controller is constructed at the front end of the constructed differential homeomorphism.

[0166] For the grid-connected control system model of this output feedback linearized grid-connected converter, a linearized controller is constructed at the front end of the built differential homeomorphism. Thus, the output vector of the output feedback linearized controller... The input vector of the differential homeomorphism The output variables of the affine nonlinear system (equivalent internal potential E or power angle δ of the grid converter) are fed back to the input of the output feedback linearization controller. In this way, feedback linearization controllers can be designed separately for the equivalent internal potential E or power angle δ of the grid converter, which helps to reduce the coupling relationship between active and reactive power.

[0167] Specifically, such as Figure 8 As shown, in the output feedback linearization controller, after output feedback, the differences between the reference value of the output variable and the time-varying output variable are denoted as output errors e1 and e2, respectively; e1 is the linearization controller G in which the equivalent internal potential linearization control branch is located. e (s) control input, e2 is the linearized controller G where the power angle linearization control branch is located. d (s) control input,

[0168] In some implementations, the output feedback linearization controller or linear control loop is constructed as shown in equation (10):

[0169]

[0170] Among them, the linearization controller G, where the equivalent internal potential linearization control branch is located e (s) includes a first-order differential element and a proportional element; the linearized controller G, where the power angle linearization control branch is located. d (s) includes a second-order differential element, a first-order differential element, and a proportional element.

[0171] Therefore, output feedback linearization controllers (including Ge(s), G) are designed for the equivalent internal potential E or power angle δ of the grid-type converter. d (s)) helps to reduce the coupling relationship between active and reactive power.

[0172] In some implementations, to increase control stability, an integral term is added to the linear control loop shown in equation (10), as shown in equation (11):

[0173]

[0174] Among them, the linearization controller G, where the equivalent internal potential linearization control branch is located e (s) includes first-order differential elements, proportional elements, and integral elements;

[0175] The linearization controller G, where the power angle linearization control branch is located d (s) includes second-order differential elements, first-order differential elements, proportional elements, and integral elements.

[0176] Furthermore, to facilitate the optimization of the linear control loop, equation (11) is transformed into the Lagrange domain, resulting in equation (12):

[0177]

[0178] From equation (12), we can obtain that in the output feedback linearization controller, the linearization controller G containing the equivalent internal potential linearization control branch is... e (s) exhibits second-order characteristics, and the linearized controller G, where the power angle linearization control branch is located, is... d (s) exhibits third-order properties.

[0179] Accordingly, the control parameters of the constructed output feedback linearization controller include: the linearization controller G containing the equivalent internal potential linearization control branch. e The first-order differential parameter k of (s) 11 proportionality constant k 12 The linearization controller G, where the power angle linearization control branch is located. e The second-order differential parameter k of (s) 21 First-order differential parameter k 22 proportionality constant k 23 .

[0180] S50: Design the control parameters of the constructed output feedback linearized controller using the design strategy of a linear controller; use the designed control parameters and the constructed output feedback linearized controller to control the grid-type converter.

[0181] In some embodiments, the control parameters in equation (12) are designed using a linear controller design strategy. The feasible combinations of control parameters are listed in equation (13), which are 5 constant values.

[0182]

[0183] In some embodiments, a Simulink simulation environment is built. Figure 8 The output feedback linearized grid-connected converter grid control system model is shown, and a fault scenario is set to verify the control accuracy and system stability of the feedback linearized controller designed in this embodiment of the invention.

[0184] like Figure 9 As shown, a system fault occurs at 0.7s; the fault is cleared at 1.4s. This is compared to the situation before using a feedback linearization controller (e.g., ...). Figure 3 or Figure 6 After the grid-connected system of the grid-connected converter shown (e.g.) Figure 8 The dynamic curves of active power (P) and reactive power (Q) of the grid-connected converter system with output feedback linearized controller shown in the figure indicate that the stability of both active and reactive power is enhanced after adopting the feedback linearized controller, reducing the power imbalance in the system caused by the error of the active and reactive power control links, and improving the system stability margin.

[0185] like Figure 10 As shown, the nonlinear control device for a grid-type converter based on feedback linearization according to an embodiment of the present invention includes:

[0186] The control system model determination unit 10 is used to simplify the grid-connected converter in the grid-connected system into a constant voltage source and simulate the rotor motion equation and excitation regulation characteristics of the synchronous machine to determine the control system model of the grid-connected system where the grid-connected converter is located.

[0187] The state-space model determination unit 20 is used to convert the control system model of the grid-connected system where the grid-connected converter is located into a state-space model, wherein the converted state-space model is an affine nonlinear system with two inputs and two outputs.

[0188] The linearization system mapping unit 30 is used to construct a differential homeomorphism for the two-input two-output affine nonlinear system; and to map the two-input two-output affine nonlinear system into a linearized system using the constructed differential homeomorphism.

[0189] The output feedback linearization controller building unit 40 is used to build an output feedback linearization controller at the front end of the constructed differential homeomorphism, and to convert the mapped linearized system into an output feedback linearization grid-connected converter control system model.

[0190] The grid-type converter control unit 50 is used to design the control parameters of the constructed output feedback linearization controller; and to control the grid-type converter using the designed control parameters and the constructed output feedback linearization controller.

[0191] The nonlinear control device for the grid-type converter based on feedback linearization has the same concept and the same technical effect as the aforementioned nonlinear control method for the grid-type converter based on feedback linearization, and can be obtained by reference, so it will not be described again.

[0192] In summary, for the scenario of grid-connected new energy power grid converters, this invention proposes a nonlinear control method and device for grid-connected power grid converters based on feedback linearization. While retaining the nonlinear characteristics of the grid-connected power grid converter, an output feedback linearization controller is constructed. By adding the feedback linearization controller, the control stability and grid connection stability of the grid-connected power grid converter are improved without decoupling active and reactive power, thus ensuring the safe and stable operation of new energy equipment connected to the grid.

[0193] Embodiments of the present invention also provide a terminal for executing the method. Please refer to... Figure 11 This illustrates a schematic diagram of a terminal provided by some embodiments of the present invention. (See reference) Figure 11 As shown, terminal 8 includes: processor 800, memory 801, bus 802 and communication interface 803, wherein processor 800, communication interface 803 and memory 801 are connected via bus 802; memory 801 stores a computer program that can run on processor 800, and when processor 800 runs the computer program, it executes the method provided by any embodiment of the present invention.

[0194] The memory 801 may include high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device. Communication between this device network element and at least one other network element is achieved through at least one communication interface 803 (which can be wired or wireless), such as the Internet, wide area network, local area network, metropolitan area network, etc.

[0195] Bus 802 can be an ISA bus, PCI bus, or EISA bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. The memory 801 is used to store programs. After receiving an execution instruction, the processor 800 executes the program. The method disclosed in any embodiment of the present invention can be applied to the processor 800, or implemented by the processor 800.

[0196] The processor 800 may be an integrated circuit chip with signal processing capabilities. In implementation, each step of the method can be completed by integrated logic circuits in the hardware of the processor 800 or by instructions in software form. The processor 800 may be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it may also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an off-the-shelf programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this invention. The general-purpose processor may be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this invention can be directly manifested as execution by a hardware decoding processor, or execution by a combination of hardware and software modules in the decoding processor. The software modules may reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. The storage medium is located in memory 801. Processor 800 reads the information in memory 801 and, in conjunction with its hardware, completes the steps of the method.

[0197] The terminal provided in this embodiment of the invention and the method in this embodiment of the invention are based on the same inventive concept and have the same beneficial effects as the methods used, operated or implemented.

[0198] like Figure 12As shown, the present invention also provides a computer-readable storage medium corresponding to the method provided in the foregoing embodiments. The computer-readable storage medium is an optical disc, on which a computer program (i.e., program product 900) is stored. When the computer program is run by a processor, it executes the method provided in any of the foregoing embodiments.

[0199] It should be noted that examples of the computer-readable storage medium may also include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other optical and magnetic storage media, which will not be described in detail here.

[0200] The computer-readable storage medium provided in the embodiments of the present invention is based on the same inventive concept as the method of the embodiments of the present invention, and has the same beneficial effects as the method adopted, run or implemented by the application stored therein.

[0201] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if any adjustments and variations of this invention fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include those modifications and variations.

Claims

1. A nonlinear control method for a network converter based on feedback linearization, characterized in that, include: The grid-connected converter in the grid-connected system is simplified as a constant voltage source, and the rotor motion equation and excitation regulation characteristics of the synchronous machine are simulated to determine the control system model of the grid-connected system where the grid-connected converter is located. The control system model of the grid-connected system where the grid-connected converter is located is converted into a state-space model. The converted state-space model is an affine nonlinear system with two inputs and two outputs. A differential homeomorphism is constructed for the two-input, two-output affine nonlinear system; the constructed differential homeomorphism is used to map the two-input, two-output affine nonlinear system into a linearized system; An output feedback linearization controller is constructed at the front end of the constructed differential homeomorphism, and the mapped linearized system is transformed into an output feedback linearized grid-connected converter control system model. The control parameters of the constructed output feedback linearization controller are designed, and the grid-type converter is controlled using the designed control parameters and the constructed output feedback linearization controller.

2. The nonlinear control method for a network converter based on feedback linearization as described in claim 1, characterized in that, The process of simplifying the grid-connected converter in the grid-connected system as a constant voltage source and simulating the rotor motion equation and excitation regulation characteristics of a synchronous machine to determine the control system model of the grid-connected system where the grid-connected converter is located includes: The grid-connected converter in the grid-connected system is simplified as a constant voltage source, where E is the equivalent internal potential of the grid-connected converter; The rotor motion equations and excitation regulation characteristics of the grid-type converter simulating a synchronous machine are controlled. The outer loop controller for the grid-type converter includes an active-frequency control branch and a reactive-voltage control branch. The active-frequency control branch is based on the acquired active power reference value P0, angular frequency reference value ω0, dynamic active power P, dynamic angular frequency ω, and first damping coefficient D. p The first feedforward coefficient J maintains system frequency stability; the reactive power-voltage control branch uses the acquired voltage reference value V0, reactive power reference value Q0, dynamic reactive power Q, equivalent internal potential E of the grid-type converter, and second damping coefficient D. q And the second feedforward coefficient K maintains voltage stability; The control system model of the grid-connected system in which the grid-connected converter is located is shown in the following equation: Where E0 is the rated equivalent internal potential of the grid-type converter; δ is the power angle; V g X is the equivalent voltage of the power grid. s This refers to the internal impedance of a grid-type converter.

3. The nonlinear control method for a network converter based on feedback linearization as described in claim 2, characterized in that, The process of converting the control system model of the grid-connected system containing the determined grid-type converter into a state-space model includes: The grid angular frequency ω, the equivalent internal electromotive force E of the grid-type converter, and the power angle δ are determined as state variables x1, x2, and x3, respectively, forming the state vector x; the reciprocals of the first feedforward coefficient J and the second feedforward coefficient K are determined as control input variables u1 and u2, respectively, forming the control input vector u; the equivalent internal electromotive force E and the power angle δ of the grid-type converter are determined as output variables y1 and y2, respectively, forming the output vector y, as shown in the following equation, where T represents the transpose operation: The control system model of the grid-connected system containing the grid-type converter is converted into a state-space model using the state vector, the control input vector, and the output vector, as shown in the following equation: The first state variable function matrix f(x) is shown in the following equation: The first control input function vector g1(x) and the second control input function vector g2(x) are shown in the following equations: The first output function vector h1(x) and the second output function vector h2(x) are shown in the following equations: h1(x)=[0x20] T h2(x)=[00x3] T ; Wherein, the inherent parameter of the first system is a = 3V g / X s The second system's inherent parameter b = 3 / X s The third system's inherent parameter c = D p / ω0;The fourth system's intrinsic parameter d=P0 / ω0+D p The fifth system's inherent parameter e = D q The sixth system's inherent parameter f = Q0 + E0D q .

4. The nonlinear control method for a grid-type converter based on feedback linearization as described in claim 3, characterized in that, The method constructs a differential homeomorphism for the two-input, two-output affine nonlinear system. The two-input, two-output affine nonlinear system is mapped to a linearized system using a constructed differential homeomorphism, including: The first-order derivatives of the output variables of the affine nonlinear system are defined as the input vectors of the diffeomorphism, denoted as... The output vector of the differential homeomorphism is determined to be the control input vector of the affine nonlinear system. The state variable of the differential homeomorphism is determined to be the state variable x of the affine nonlinear system; The expression for determining the differential homeomorphism is shown below: The second state variable function matrix E(x) is shown in the following equation: Third state variable function matrix A -1 (x) is shown in the following formula: The constructed differential homeomorphism is placed at the front end of the affine nonlinear system, and the two-input, two-output affine nonlinear system is mapped to a linearized system, so that the constructed differential homeomorphism and the affine nonlinear system together constitute a linearized grid-connected converter control system model.

5. The nonlinear control method for a grid-type converter based on feedback linearization as described in claim 4, characterized in that, The step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism, and converting the mapped linearized system into an output feedback linearized grid-connected converter control system model, includes: For the grid-connected control system model of a linearized grid-connected converter, an output feedback linearized controller is constructed; wherein, the output variable of the output feedback linearized controller is the input variable of the differential homeomorphism, and the output variable of the affine nonlinear system is fed back to the control input terminal of the output feedback linearized controller; The output feedback linearization controller includes an equivalent internal potential linearization control branch and a power angle linearization control branch.

6. The nonlinear control method for a grid-type converter based on feedback linearization as described in claim 5, characterized in that, The step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism includes: The constructed output feedback linearization controller is shown in the following equation: Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij These are the constant coefficients of each element within the linearization controller, where i is 1 or 2, and j is 1 or 2.

7. The nonlinear control method for a grid-type converter based on feedback linearization as described in claim 5, characterized in that, The step of constructing an output feedback linearization controller at the front end of the constructed differential homeomorphism includes: The constructed output feedback linearization controller is shown in the following equation: Where, e1 is the internal potential control error of the equivalent internal potential linearization control branch in the output feedback linearization controller, and e2 is the power angle control error of the power angle linearization control branch in the output feedback linearization controller; k ij These are the constant coefficients of each element within the linearization controller, where i is 1 or 2, and j is 1, 2, or 3.

8. A nonlinear control device for a grid-type converter based on feedback linearization, characterized in that, include: The control system model determination unit is used to simplify the grid-connected converter in the grid-connected system into a constant voltage source and simulate the rotor motion equation and excitation regulation characteristics of the synchronous machine, thereby determining the control system model of the grid-connected system in which the grid-connected converter is located. The state-space model determination unit is used to convert the control system model of the grid-connected system where the grid-connected converter is located into a state-space model. The converted state-space model is an affine nonlinear system with two inputs and two outputs. A linearized system mapping unit is used to construct a differential homeomorphism for the two-input, two-output affine nonlinear system; and to map the two-input, two-output affine nonlinear system into a linearized system using the constructed differential homeomorphism. The output feedback linearization controller construction unit is used to construct an output feedback linearization controller at the front end of the constructed differential homeomorphism, and to convert the mapped linearized system into an output feedback linearization grid-connected converter control system model. The grid-type converter control unit is used to design the control parameters of the constructed output feedback linearization controller; the designed control parameters and the constructed output feedback linearization controller are used to control the grid-type converter.

9. A terminal, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the method as claimed in any one of claims 1 to 7.

10. A computer storage medium, characterized in that, The device stores computer-executable instructions for performing the method as described in any one of claims 1 to 7.

Images