A method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system

Abstract

The present invention discloses a method for determining the cause of subsynchronous oscillation of a doubly-fed wind power grid-connected system in the field of subsynchronous oscillation analysis research of power systems, comprising: firstly, dividing the doubly-fed wind power grid-connected system into a doubly-fed wind turbine subsystem and a transmission line subsystem; secondly, obtaining the subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem and the transmission line subsystem; then, analyzing the obtained subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem and the transmission line subsystem, and determining the properties of each term in the subsynchronous modal energy balance equation; finally, determining the possible cause of subsynchronous oscillation caused by the doubly-fed wind power grid-connected system according to the properties of the energy term. This method can provide a mechanism explanation for the subsynchronous oscillation problem of the doubly-fed wind power grid-connected system from an energy perspective, provide theoretical support for the source tracing and positioning of the subsynchronous oscillation of the doubly-fed wind power grid-connected system, and provide support for the determination of the cause of subsynchronous oscillation in complex scenes and multiple working conditions of large-scale wind farms.

Description

Technical Field

[0001] The present invention relates to the research field of subsynchronous oscillation analysis of power systems, and in particular to a method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system. Background Art

[0002] As the scale of wind power grid connection increases, subsynchronous oscillation caused by series-compensated double-fed wind turbines is becoming more frequent. At present, there is a basic consensus on subsynchronous oscillation accidents that occur in the wind farm transmission system through series compensation, and it is believed that the interaction between the wind power control system and the series compensation capacitor is the root cause of the oscillation.

[0003] At present, the traditional research methods for subsynchronous oscillations are mainly based on eigenvalue analysis and impedance method. However, such methods are only applicable to analyzing the system characteristics at a certain operating point or several independent equilibrium points using equivalent wind farms. It is difficult to provide support for the determination of the causes of subsynchronous oscillations in complex scenarios and multiple operating conditions of large-scale wind farms. Summary of the invention

[0004] In view of the deficiencies in the prior art, an object of the present invention is to provide a method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system, so as to solve the problems raised in the above background technology.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system, comprising:

[0007] Firstly, the doubly-fed wind power grid-connected system is divided into a doubly-fed wind turbine subsystem and a transmission line subsystem.

[0008] Secondly, the subsynchronous modal energy balance equations of the doubly-fed wind turbine subsystem and the transmission line subsystem are obtained;

[0009] Then, the subsynchronous modal energy balance equations of the double-fed wind turbine subsystem and the transmission line subsystem are analyzed to determine the properties of each term in the subsynchronous modal energy balance equation;

[0010] Finally, the possible causes of subsynchronous oscillations in the doubly-fed wind power grid-connected system are determined based on the properties of the energy term.

[0011] Preferably, the subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem is calculated as follows:

[0012] First, define the subsynchronous modal energy stored in the doubly fed wind turbine, as shown in formula (1):

[0013]

[0014] In the formula,

[0015] Δx1=[Δψ ds Δψ qs Δψ dr Δψ qr JΔω r L g Δi dg L g Δi qg CΔu dc ] T

[0016]

[0017] Then the change rate of the subsynchronous modal energy stored in the doubly fed wind turbine subsystem is obtained, as shown in formula (2):

[0018]

[0019] The port variable Δi d ,Δi q ,Δu ds ,Δu qs Transform from the dq coordinate system to the xy coordinate system, as shown in formula (3):

[0020]

[0021] Preferably, the subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem is obtained by the following method:

[0022] Substitute equation (3) into equation (2) and integrate both sides from time 0 to time t, as shown in equation (4):

[0023] W 1port =W 1SSO +W 1diss +W 1gen +W 1conv +W 1PE (4)

[0024] In the formula,

[0025]

[0026] Preferably, the subsynchronous modal energy balance equation of the transmission line subsystem is calculated as follows:

[0027] First, define the subsynchronous modal energy stored in the transmission line subsystem as shown in formula (5):

[0028]

[0029] In the formula,

[0030]

[0031] Then the rate of change of the subsynchronous modal energy stored in the transmission line subsystem is obtained, as shown in formula (6):

[0032]

[0033] Finally, the subsynchronous modal energy balance equation of the transmission line subsystem containing series compensation capacitor is obtained, as shown in formula (7):

[0034] W 2port =W 2port1 +W 2port2 =W 2SSO +W 2diss (7)

[0035] In the formula,

[0036]

[0037] Preferably, the properties of each energy term of the subsynchronous modal energy balance equation of the doubly fed wind turbine subsystem are analyzed:

[0038] In formula (4), W 1port The subsynchronous modal energy of the port flowing into the double-fed wind turbine subsystem from the external system is converted into five types of energy: W 1SSO ,W 1PE ,W 1gen ,W 1conv ,W 1diss .

[0039] Preferably, the properties of each energy term of the subsynchronous modal energy balance equation of the transmission line subsystem are analyzed:

[0040] In formula (7), W 2port is the total port subsynchronous mode energy flowing into the transmission line subsystem from the external system, which is converted into two types of energy: W 2SSO and W 2diss .

[0041] Preferably, the possible causes of subsynchronous oscillation caused by the doubly-fed wind power grid-connected system are determined according to the properties of the energy term as follows:

[0042] For the doubly-fed wind turbine subsystem, the induction motor, phase-locked loop, and converter are the causes of oscillation.

[0043] For the transmission line subsystem, there is no inducement to oscillate.

[0044] Beneficial effects of the present invention:

[0045] 1. The method for determining the cause of subsynchronous oscillation of the present invention can provide a mechanism explanation for the subsynchronous oscillation problem of the doubly-fed wind power grid-connected system from an energy perspective, provide theoretical support for the tracing and positioning of the subsynchronous oscillation of the doubly-fed wind power grid-connected system, and provide support for the determination of the cause of subsynchronous oscillation in complex scenarios and multiple working conditions of large-scale wind farms. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0047] Figure 1 It is a flow chart of the method for determining the cause of subsynchronous oscillation of the present invention;

[0048] Figure 2 It is a schematic diagram of the structure of the double-fed wind power grid-connected system adopted by the present invention. DETAILED DESCRIPTION

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

[0050] See also Figure 1 As shown, the present invention provides a method for determining the cause of subsynchronous oscillation of a doubly-fed wind power grid-connected system. First, the doubly-fed wind power grid-connected system is divided into a doubly-fed wind turbine subsystem and a transmission line subsystem. The subsynchronous modal energy balance equations of the doubly-fed wind turbine subsystem and the transmission line subsystem are obtained by calculation. Then, the subsynchronous modal energy balance equations of the doubly-fed wind turbine subsystem and the transmission line subsystem are analyzed to determine the properties of each term in the subsynchronous modal energy balance equation. Finally, the possible cause of subsynchronous oscillation caused by the doubly-fed wind power grid-connected system is determined according to the properties of the energy terms.

[0051] Figure 2 The structure diagram of the doubly-fed wind power grid-connected system is shown in FIG. 1 , which can be divided into a doubly-fed wind turbine subsystem and a transmission line subsystem.

[0052] Among them, i d and i q It represents the dq axis component of the total output current of the generator side and the grid side, i ds ,i qs ,i dr ,i qrare the dq axis components of the stator current and rotor current of the doubly fed wind turbine, i dg ,i qg are the dq axis components of the grid-side current of the double-fed wind turbine, X C is the capacitive reactance of the series compensation capacitor, X T is the equivalent reactance of the transformer, R L is the line resistance, X L is the line reactance.

[0053] The present invention comprises the following steps:

[0054] Step 1: Divide the doubly-fed wind power grid-connected system into a doubly-fed wind turbine subsystem and a transmission line subsystem;

[0055] Step 2: Obtain the subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem and the transmission line subsystem;

[0056] The subsynchronous modal energy stored in the doubly fed wind turbine is defined as shown in formula (1), which refers to the energy obtained by multiplying the two components of the same mode:

[0057]

[0058] in,

[0059] Δx1=[Δψ ds Δψ qs Δψ dr Δψ qr JΔω r L g Δi dg L g Δi qg CΔu dc ] T

[0060]

[0061] i dg ,i qg are the dq axis components of the grid-side current of the doubly-fed wind turbine, ψ ds ,ψ qs , ψ dr , ψ qr They are the dq axis components of the stator flux and rotor flux of the doubly fed wind turbine respectively. r is the angular velocity of the synchronous magnetic field and the angular velocity of the doubly fed wind turbine rotor, J represents the inertia of the doubly fed wind turbine shaft system. C is the DC side capacitance, u dc is the DC capacitor voltage. L s ,L r are the equivalent two-phase winding self-inductance of the stator in the dq coordinate system and the equivalent two-phase winding self-inductance of the rotor in the dq coordinate system, Lm is the mutual inductance between the stator and rotor coaxial equivalent windings in the dq coordinate system, L g is the line inductance of the grid-side converter. Δ represents the subsynchronous component of the corresponding variable.

[0062] Then the change rate of the subsynchronous modal energy stored in the doubly fed wind turbine subsystem can be obtained as:

[0063]

[0064] u ds ,u qs are the dq axis components of the stator voltage of the doubly fed wind turbine, i ds ,i qs ,i dr ,i qr are the dq axis components of the stator current and rotor current of the doubly fed wind turbine, i d and i q It represents the dq axis component of the total output current on the generator side and the grid side. D is the damping of the doubly fed fan rotor, R s ,R r ,R g They are the stator resistance of the doubly-fed wind turbine, the rotor resistance of the doubly-fed wind turbine and the line resistance of the grid-side converter. dg ,s dg are the dq axis components of the modulation signal of the grid-side converter of the doubly-fed wind turbine, s dr ,s qr They are respectively the dq axis components of the modulation signal of the machine-side converter of the doubly fed wind turbine.

[0065] In order to reflect the impact of the external network on the doubly fed wind turbine during subsynchronous oscillation, the port variable Δi d ,Δi q ,Δu ds ,Δu qs By transforming the dq coordinate system to the xy coordinate system, we can obtain:

[0066]

[0067] Among them, Δu xs ,Δu ys are the xy-axis subsynchronous components of the stator voltage of the doubly fed wind turbine, Δi x ,Δi y They are the xy-axis subsynchronous components of the total output current on the generator side and the grid side of the doubly fed wind turbine, and Δδ is the subsynchronous component of the phase-locking angle of the doubly fed wind turbine.

[0068] Substituting equation (4) into equation (3) and integrating both sides from time 0 to time t, the subsynchronous modal energy balance equation of the doubly fed wind turbine subsystem can be obtained:

[0069] W 1port=W 1SSO +W 1diss +W 1gen +W 1conv +W 1PE (5)

[0070] in,

[0071]

[0072] The subsynchronous modal energy stored in the transmission line subsystem is defined as shown in formula (6):

[0073]

[0074] in,

[0075]

[0076] u cx ,u cy are the x and y axis components of the series compensation capacitor voltage, i x ,i y are the x and y axis components of the line current respectively. C is the capacitive reactance of the series compensation capacitor, X T is the equivalent reactance of the transformer, X L is the line reactance, X ΣL =X T +X L Δ represents the subsynchronous component of the corresponding variable.

[0077] Then, the rate of change of the subsynchronous modal energy stored in the transmission line subsystem can be obtained, as shown in formula (7):

[0078]

[0079] Among them, E Bx ,E By are the x and y axis components of the infinite grid bus voltage, u xs ,u ys are the x and y axis components of the fan stator voltage, R L is the line resistance, and Δ represents the subsynchronous component of the corresponding variable.

[0080] Further, the subsynchronous modal energy balance equation of the transmission line subsystem containing series compensation capacitors is obtained as follows:

[0081] W 2port =W 2port1 +W 2port2 =W 2SSO +W 2diss (8)

[0082] in,

[0083]

[0084] Step 3: Analyze the subsynchronous modal energy balance equation of the doubly-fed wind turbine subsystem and the transmission line subsystem, and determine the properties of each term in the subsynchronous modal energy balance equation;

[0085] For the subsynchronous modal energy balance equation of the doubly fed wind turbine subsystem shown in equation (5), W 1port is the subsynchronous modal energy of the port flowing into the double-fed wind turbine subsystem from the external system, which can be converted into five types of energy: W 1SSO is the subsynchronous modal energy in the doubly fed wind turbine subsystem, which is a conservative term (independent of the integration path); W 1PE ,W 1gen ,W 1conv ,W 1diss They are the change of subsynchronous modal energy potential of the doubly fed wind turbine subsystem, the subsynchronous modal energy of the induction generator, the subsynchronous modal energy of the converter system, and the subsynchronous modal energy of the doubly fed wind turbine resistance and shaft damping dissipation. These four energies are non-conservative terms, among which W 1diss Always positive.

[0086] For the subsynchronous modal energy balance equation of the transmission line subsystem shown in equation (8), W 2port is the total port subsynchronous modal energy flowing into the transmission line subsystem from the external system, which can be converted into two types of energy: W 2SSO is the subsynchronous mode energy stored in the transmission line subsystem, which is a conservative term; W 2diss is the subsynchronous modal energy dissipated by the line resistance and is a non-conservative term that is always positive.

[0087] Step 4: Determine the possible causes of subsynchronous oscillations in the doubly-fed wind power grid-connected system based on the properties of the energy term;

[0088] For the doubly-fed wind turbine subsystem, due to W 1PE ,W 1gen ,W 1conv Both can be positive or negative, providing positive damping when positive and negative damping when negative. Therefore, it can be considered that the induction motor, phase-locked loop, and inverter are the causes of oscillation.

[0089] For the transmission line subsystem, due to W 2SSO is a conservative term, and W 2diss It is a non-conservative term that is always positive, so there is no possibility of inducing oscillation.

[0090] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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 in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system, characterized in that: include: Firstly, the doubly-fed wind power grid-connected system is divided into a doubly-fed wind turbine subsystem and a transmission line subsystem. Secondly, the subsynchronous modal energy balance equations of the doubly-fed wind turbine subsystem and the transmission line subsystem are obtained; Then, the subsynchronous modal energy balance equations of the double-fed wind turbine subsystem and the transmission line subsystem are analyzed to determine the properties of each term in the subsynchronous modal energy balance equation; Finally, the possible causes of subsynchronous oscillation in the doubly-fed wind power grid-connected system are determined based on the properties of the energy term; The subsynchronous modal energy stored in the doubly fed wind turbine is shown in formula (1): in, Δx1=[Δψ ds Dp qs Dp dr Dp qr JSee r L g Yes dg L g Yes qg CΔu dc ] T In the formula, i dg ,i qg are the dq axis components of the grid-side current of the doubly-fed wind turbine, ψ ds ,ψ qs , ψ dr , ψ qr are the dq axis components of the stator flux and rotor flux of the doubly fed wind turbine respectively; ω r is the angular velocity of the synchronous magnetic field and the angular velocity of the doubly fed wind turbine rotor, J represents the inertia of the doubly fed wind turbine shaft system; C is the DC side capacitance, u dc is the DC capacitor voltage; L s ,L r are the equivalent two-phase winding self-inductance of the stator in the dq coordinate system and the equivalent two-phase winding self-inductance of the rotor in the dq coordinate system, L m is the mutual inductance between the stator and rotor coaxial equivalent windings in the dq coordinate system, L g is the line inductance of the grid-side converter; Δ represents the subsynchronous component of the corresponding variable; The rate of change of the subsynchronous modal energy stored in the doubly fed wind turbine subsystem is shown in formula (2): In the formula, u ds ,u qs are the dq axis components of the stator voltage of the doubly fed wind turbine, i ds ,i qs ,i dr ,i qr are the dq axis components of the stator current and rotor current of the doubly fed wind turbine, i d and i q represents the dq-axis component of the total output current on the generator side and the grid side; D is the damping of the doubly fed fan rotor, R s ,R r ,R g They are the stator resistance of the doubly-fed wind turbine, the rotor resistance of the doubly-fed wind turbine and the line resistance of the grid-side converter; s dg ,s dg are the dq axis components of the modulation signal of the grid-side converter of the doubly-fed wind turbine, s dr ,s qr They are the dq axis components of the modulation signal of the converter on the machine side of the doubly fed wind turbine respectively; The port variable Δi d ,Δi q ,Δu ds ,Δu qs Transform from the dq coordinate system to the xy coordinate system, as shown in formula (3): In the formula, Δu xs ,Δu ys are the xy-axis subsynchronous components of the stator voltage of the doubly fed wind turbine, Δi x ,Δi y are the xy-axis subsynchronous components of the total output current on the generator side and the grid side of the doubly fed wind turbine, and Δδ is the subsynchronous component of the phase-locking angle of the doubly fed wind turbine; The subsynchronous modal energy balance equation of the doubly fed wind turbine subsystem is shown in formula (4): IN 1port =In 1SSO +W 1diss +W 1gen +W 1conv +W 1PE (4) in, ； In the formula (4), W 1port is the subsynchronous modal energy of the port flowing into the double-fed wind turbine subsystem from the external system, which is converted into five types of energy: W 1SSO ,W 1PE ,W 1gen ,W 1conv ,W 1diss ; The subsynchronous modal energy balance equation of the transmission line subsystem is calculated as follows: First, define the subsynchronous modal energy stored in the transmission line subsystem as shown in formula (5): in, In the formula, u cx ,u cy are the x and y axis components of the series compensation capacitor voltage, i x ,i y are the x and y axis components of the line current, respectively. C is the capacitive reactance of the series compensation capacitor, X T is the equivalent reactance of the transformer, X L is the line reactance, X ΣL =X T +X L ; Then the rate of change of the subsynchronous modal energy stored in the transmission line subsystem is obtained, as shown in formula (6): In the formula, E Bx ,E By are the x and y axis components of the infinite grid bus voltage, u xs ,u ys are the x and y axis components of the fan stator voltage, R L is the line resistance; Finally, the subsynchronous modal energy balance equation of the transmission line subsystem containing series compensation capacitors is obtained, as shown in equation (7): IN 2port =In 2port1 +W 2port2 =In 2SSO +W 2diss (7) in, In the formula (7), W 2port is the total port subsynchronous mode energy flowing into the transmission line subsystem from the external system, which is converted into two types of energy: W 2SSO and W 2diss .

2. A method for determining the cause of subsynchronous oscillation in a doubly-fed wind power grid-connected system according to claim 1, characterized in that: The causes of subsynchronous oscillation in the doubly-fed wind power grid-connected system are determined according to the properties of the energy term as follows: For the doubly-fed wind turbine subsystem, the induction motor, phase-locked loop, and converter are the causes of oscillation; For the transmission line subsystem, there is no inducement to oscillate.

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