Doubly-fed fan modeling method based on full-electromagnetic transient simulation platform

Abstract

The invention provides a doubly-fed fan modeling method based on a full-electromagnetic transient simulation platform, and the method is characterized in that the method comprises the steps: describing captured wind energy through building a wind turbine model, and tracking a directional voltage phase through building a phase-locked loop model; establishing a shafting model by enabling a wind turbine, a gear box and a generator rotor to be equivalent to three mass blocks; power and voltage control is realized by establishing a generator model, a network side filter model, an inverter and a control model of the inverter; a power transmission line model; and finally, packaging the established model into a black box model. The invention provides a modeling method of a doubly-fed fan, which can improve the simulation efficiency and increase the stability of wind power generation access to a power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and particularly to a modeling method for a doubly-fed wind turbine based on a full electromagnetic transient simulation platform. Background Art

[0002] With the continuous exacerbation of the shortage of traditional fossil energy and environmental deterioration problems, the utilization and development of energy must shift from traditional energy to clean energy such as renewable energy. The modeling of wind turbines is the basis for studying the operation and control of wind farms connected to the power grid. For traditional technologies, it is becoming increasingly unable to cope with the acceptance of ultra-large-scale renewable energy: on the one hand, limited by the power system's consumption capacity, most renewable energy has not been effectively utilized; on the other hand, new energy power generation such as wind power and solar power is intermittent and random, belonging to intermittent power sources, and traditional parallel power technologies are not applicable. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a modeling method for a doubly-fed wind turbine based on a full electromagnetic transient simulation platform to solve at least the above problems.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A modeling method for a doubly-fed wind turbine based on a full electromagnetic transient simulation platform, the method comprising:

[0006] Step 1: Establish a wind turbine model, a phase-locked loop model, a shafting model, a generator model, a grid-side filter model, an inverter and its control model, and a transmission line model;

[0007] The wind turbine model converts energy by intercepting part of the kinetic energy of the flowing air, and the wind turbine model includes a wind turbine aerodynamic model and a pitch angle control model;

[0008] The wind turbine aerodynamic model uses the Betz formula to describe the wind energy captured by the wind turbine, and the equation is:

[0009] P Aero = 0.5C P (λ,β)Aρv 3

[0010]

[0011] Wherein, P Aero is the output power of the wind turbine, P base is the reference power of the DFIG, C P is the wind energy utilization coefficient of the wind turbine, the magnitude of which is determined by the tip speed λ and the pitch angle β, A is the area swept by the wind wheel, ρ is the air density, v is the wind speed, R is the radius of the wind wheel, T mis the mechanical torque of wind energy conversion on the hub, ω t is the rotational speed of the generator rotor;

[0012] The pitch angle control model uses the pitch angle to control the mechanical power and the speed controller to control the electromagnetic power to achieve the power balance of the DFIG system;

[0013] Step 2: Package the model established in Step 1 into a black box model.

[0014] Furthermore, the phase-locked loop model in Step 1 tracks the phase of the oriented voltage through the phase-locked loop, and its dynamic equation is:

[0015]

[0016] where, θ PLL is the angle by which the observed voltage leads the d-axis of the synchronous rotating coordinate system, x PLL is the error accumulation of tracking the stator q-axis voltage, u qs is the stator q-axis voltage, ω PLL is the angular frequency measured by the phase-locked loop, ω b is the grid angular frequency.

[0017] Furthermore, the shafting model in Step 1 models the wind turbine, gearbox, and generator rotor as a three-mass block model. The dynamic equation of the three-mass block model is:

[0018]

[0019] where, H t , H h , H r respectively represent the inertia constants of the concentrated equivalent mass blocks of the wind turbine, gearbox, and generator. D t , D h , D r respectively represent the damping coefficients of the three mass blocks. D th , D hr respectively represent the damping coefficients between the wind turbine and the gearbox, and between the gearbox and the generator. K th , K hr respectively are the equivalent stiffness coefficients of the low-speed shaft between the wind turbine and the gearbox, and the high-speed shaft between the gearbox and the generator. θ a , θ b respectively are the torsional angular displacements between the wind turbine and the gearbox, and between the gearbox and the generator. ω t , ω h , ω r respectively are the rotational speeds of the wind turbine, gearbox, and generator. T m , T e respectively are the mechanical torque and the electromagnetic torque.

[0020] Furthermore, in step 4, the generator model uses a two-phase synchronous rotating coordinate system to replace the three-phase stationary coordinate system for decoupling and simplifying the model. The generator model includes stator-rotor voltage equations, flux linkage equations, and electromagnetic torque equations;

[0021] The rotor voltage equation is:

[0022]

[0023] where u s and u r are the stator and rotor voltages of the generator, ψ s and ψ r are the stator and rotor flux linkages of the generator, and i s and i r are the stator and rotor currents of the generator;

[0024] The flux linkage equation is:

[0025]

[0026] where L Is and L Ir are the stator and rotor leakage inductances, and L m is the mutual inductance between the stator and rotor;

[0027] The electromagnetic torque equation is:

[0028] T e = L m (i qs i dr - i ds i qr ).

[0030] Furthermore, step 5 is specifically as follows: The grid-side filter is divided into an inductor branch and a capacitor branch. The equation of the inductor branch is:

[0031]

[0032] where u dg and u qg are the d-axis and q-axis voltages output by the grid-side converter, and i dg and i qg are the d-axis and q-axis currents of the grid-side filter;

[0033] The equation of the capacitor branch is:

[0034]

[0035] where U d_cl and U q_cl are the d-axis and q-axis components of the voltage across the capacitor, and idl and i ql are the d - axis and q - axis components of the inductive current of the transmission line.

[0036] Furthermore, in step 6, the inverter and its control model include a DC capacitor model, a rotor - side converter control model, and a grid - side converter control model;

[0037] The DC capacitor model is used to maintain the balance of the DC capacitor voltage, and its equation is:

[0038]

[0039] where U dc is the voltage across the DC - side capacitor;

[0040] The rotor - side converter control model indirectly adjusts the output power of the stator side by controlling the rotor excitation current, and the equation is:

[0041]

[0042] The grid - side converter control model is used to maintain the stability of the DC bus voltage and achieve the control of the AC - side power factor, and the equation is:

[0043]

[0044] Furthermore, step 7 is specifically: equivalent the transmission line transformer to an RL model, and the dynamic equation is:

[0045]

[0046] where u d_pcc , u q_pcc are the d - axis and q - axis voltages at the PCC point respectively.

[0047] Compared with the prior art, the beneficial effects of the present invention are:

[0048] The present invention provides a modeling method for doubly - fed wind turbines based on a full - electromagnetic transient simulation platform. By establishing a wind turbine model to describe the captured wind energy, by establishing a phase - locked loop model to track the orientation voltage phase, by establishing a generator model, a grid - side filter model, and an inverter and its control model to achieve power and voltage control, and by establishing a shafting model by equivalent the wind turbine, gearbox, and generator rotor to a three - mass block, it can improve the simulation accuracy and efficiency, and increase the stability of wind power access to the grid. Description of the Drawings

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only the preferred embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0050] Figure 1 is the overall structural schematic diagram of the system in the embodiment of the present invention;

[0051] Figure 2 is the structural schematic diagram of the wind turbine model in the embodiment of the present invention;

[0052] Figure 3 is the structural schematic diagram of the generator model in the embodiment of the present invention;

[0053] Figure 4 is the structural schematic diagram of the grid-side filter model in the embodiment of the present invention;

[0054] Figure 5 is the structural schematic diagram of the inverter and its control model in the embodiment of the present invention. Detailed implementation manners

[0055] The principles and features of the present invention will be described below with reference to the accompanying drawings. The listed embodiments are only used to explain the present invention and are not used to limit the scope of the present invention.

[0056] Refer to Figure 1 , the present invention provides a modeling method for a doubly-fed wind turbine based on a full electromagnetic transient simulation platform. The method includes:

[0057] Step 1: Establish a wind turbine model, a phase-locked loop model, a shafting model, a generator model, a grid-side filter model, an inverter and its control model, and a transmission line model;

[0058] The wind turbine model in Step 1 converts energy by intercepting part of the kinetic energy of the flowing air, including a wind turbine aerodynamic model and a pitch angle control model;

[0059] The wind turbine aerodynamic model uses the Betz formula to describe the wind energy captured by the wind turbine. The equation is:

[0060] P Aero = 0.5C P (λ,β)Aρv 3

[0061]

[0062] where P Aero is the output power of the wind turbine, P base is the base power of the DFIG, CP is the wind energy utilization coefficient of the wind turbine, the magnitude of which is determined by the tip speed ratio λ and the pitch angle β. A is the area swept by the wind turbine rotor, ρ is the air density, v is the wind speed, R is the radius of the wind turbine rotor, and T m is the mechanical torque converted from wind energy on the hub, and ω t is the rotational speed of the generator rotor;

[0063] Exemplarily, the wind turbine is an important part in the DFIG system to convert wind energy into mechanical energy, and the energy conversion is completed by intercepting part of the kinetic energy of the flowing air. Therefore, the wind turbine model not only determines the output power of the entire wind power system, but also directly affects the operating performance of the wind turbine generator set, and is a key functional component in the DFIG system.

[0064] The pitch angle control model uses the pitch angle to control the mechanical power and the speed controller to control the electromagnetic power to achieve the power balance of the DFIG system.

[0065] Exemplarily, in order to make the wind energy utilization rate of the wind turbine controllable within a certain range and ensure that the DFIG output power is limited within the rated power, the wind turbine usually needs to be installed with pitch angle control. To achieve the power balance of the DFIG system, it can be completed by using the pitch angle to control the mechanical power or the speed controller to control the electromagnetic power. When the generator speed exceeds the rated speed, in order to suppress the fluctuations caused by the separate adjustment of the speed controller, the pitch angle control is started for control; when the DFIG output power exceeds the rated power, the pitch angle control will adjust the windward direction of the blade, reduce the blade angle of attack, so that the output active power of the generator is maintained at the rated power, and prevent forced shutdown due to excessive wind speed.

[0066] In step 1, the phase-locked loop model tracks the phase of the oriented voltage through the phase-locked loop, and its dynamic equation is:

[0067]

[0068] where θ PLL is the angle by which the observed voltage leads the d-axis of the synchronous rotating coordinate system, x PLL is the error accumulation of tracking the stator q-axis voltage, u qs is the stator q-axis voltage, ω PLL is the angular frequency measured by the phase-locked loop, and ω b is the grid angular frequency.

[0069] Exemplarily, in order to obtain good control effects, the DFIG system adopts stator voltage-oriented vector control, that is, the d-axis of the rotating reference coordinate system coincides with the stator voltage. The present invention selects a phase-locked loop to track the phase of the oriented voltage.

[0070] In Step 1, the shafting model models the wind turbine, gearbox, and generator rotor as a three-mass model. The dynamic equations of the three-mass model are as follows:

[0071]

[0072] Among them, H t 、H h 、H r represent the inertia constants of the lumped equivalent mass blocks of the wind turbine, gearbox, and generator respectively. D t 、D h 、D r represent the damping coefficients of the three mass blocks respectively. D th 、D hr represent the damping coefficients between the wind turbine and the gearbox, and between the gearbox and the generator respectively. K th 、K hr are the equivalent stiffness coefficients of the low-speed shaft between the wind turbine and the gearbox, and the high-speed shaft between the gearbox and the generator respectively. θ a 、θ b are the torsional angular displacements between the wind turbine and the gearbox, and between the gearbox and the generator respectively. ω t 、ω h 、ω r are the rotational speeds of the wind turbine, gearbox, and generator respectively. T m 、T e are the mechanical torque and electromagnetic torque respectively.

[0073] Exemplarily, to study the dynamic characteristics of the shafting, the shafting can be concentrated at different positions by the lumped mass method to construct different shafting mass models. For example, by respectively equivalent the three blades, hub, gearbox, and generator rotor, etc., a six-mass model of the shafting can be obtained. However, since the six-mass model is too complex and its unbalanced blade torque has no effect on the transient behavior of the wind power system, the unbalanced characteristics of its blades can be ignored, and a single mass block is used to concentrate and equivalent the mass model of the three blades to obtain a four-mass model of the shafting. In the four-mass model, the blades and the hub are further concentrated to obtain a three-mass model of the shafting.

[0074] In Step 1, the generator model uses a two-phase synchronous rotating coordinate system to replace the three-phase stationary coordinate system for decoupling and simplifying the model. The generator model includes stator-rotor voltage equations, flux linkage equations, and electromagnetic torque equations;

[0075] The rotor voltage equation is:

[0076]

[0077] Among them, u s and u rThey are the stator and rotor voltages of the generator, ψ s and ψ r They are the stator and rotor flux linkages of the generator, i s and i r They are the stator and rotor currents of the generator;

[0078] The flux linkage equation is:

[0079]

[0080] where, L Is 、L Ir are the stator and rotor leakage inductances respectively, and L m is the mutual inductance between the stator and rotor;

[0081] The electromagnetic torque equation is:

[0082] T e =L m (i qs i dr -i ds i qr )。

[0084] In step 1, the grid-side filter model divides the grid-side filter into an inductor branch and a capacitor branch. The equation of the inductor branch is:

[0085]

[0086] where, u dg 、u qg are the d-axis and q-axis voltages output by the grid-side converter, and i dg 、i qg are the d-axis and q-axis currents of the grid-side filter;

[0087] The equation of the capacitor branch is:

[0088]

[0089] where, U d_cl 、U q_cl are the d-axis and q-axis components of the voltage across the capacitor, and i dl 、i ql are the d-axis and q-axis components of the inductor current of the transmission line.

[0090] Exemplarily, the grid-side filter adopts an LC low-pass filter.

[0091] In step 1, the inverter and its control model include a DC capacitor model, a rotor-side converter control model, and a grid-side converter control model;

[0092] Exemplarily, when the output active powers of the rotor-side converter and the grid-side converter are unbalanced, the unbalanced power will cause fluctuations in the DC capacitor voltage.

[0093] The DC capacitor model is used to maintain the balance of the DC capacitor voltage, and its equation is:

[0094]

[0095] where U dc is the voltage across the DC-side capacitor;

[0096] The rotor-side converter control model indirectly realizes the regulation of the stator-side output power by controlling the rotor excitation current, and the equation is:

[0097]

[0098] Exemplarily, considering the coupling relationship between the stator and rotor currents of the doubly-fed motor, the rotor-side converter can indirectly realize the regulation of the stator-side output power by controlling the rotor excitation current. The control functions of the rotor-side converter are: to achieve the maximum power point tracking of wind energy by controlling the generating speed or active power; to control the reactive power output by the doubly-fed motor to ensure the operation stability of the grid connected.

[0099] The grid-side converter control model is used to maintain the stability of the DC bus voltage and realize the control of the AC-side power factor, and the equation is:

[0100]

[0101] Exemplarily, due to the decoupling effect of the DC link, the grid-side converter is independent of the rotor-side converter in function, and its main function is to maintain the stability of the DC bus voltage and realize the control of the AC-side power factor.

[0102] Step 7 is specifically: equivalent the transmission line and the transformer to an RL model, and the dynamic equation is:

[0103]

[0104] where u d_pcc and u q_pcc are the voltages at the d-axis and q-axis of the PCC point respectively.

[0105] Exemplarily, due to the large excitation impedance of the transformer, in order to reduce the order of the transmission line model, the transformer excitation branch can be ignored, and the transmission line and the transformer can be equivalent to an RL model.

[0106] Step 2: Package the model established in Step 1 into a black-box model.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform, characterized in that: The method comprises: Step 1: Establish wind turbine model, phase-locked loop model, shaft system model, generator model, grid-side filter model, inverter and its control model, and transmission line model; The wind turbine model converts energy by intercepting part of the kinetic energy of the flowing air, and the wind turbine model includes a wind turbine aerodynamic model and a pitch angle control model; The wind turbine aerodynamic model uses the Betz formula to describe the wind energy captured by the wind turbine. The equation is: P Aero =0.5C P (λ,β)Arv 3 Among them, P Aero is the output power of the wind turbine, P base is the reference power of DFIG, C P is the wind energy utilization coefficient of the wind turbine, which is determined by the blade tip speed λ and the pitch angle β, A is the area swept by the wind rotor, ρ is the air density, v is the wind speed, R is the radius of the wind rotor, and T m is the mechanical torque converted from wind energy on the hub, ω t is the generator rotor speed; The pitch angle control model uses the pitch angle to control the mechanical power and the speed controller to control the electromagnetic power to achieve the power balance of the DFIG system; Step 2: Encapsulate the model built in step 1 into a black box model.

2. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform according to claim 1, characterized in that: The phase-locked loop model in step 1 tracks the directional voltage phase through a phase-locked loop, and its dynamic equation is: Among them, θ PLL is the angle between the observed voltage lead and the d-axis of the synchronous rotating coordinate system, x PLL To track the error accumulation of the stator q-axis voltage, u qs is the stator q-axis voltage, ω PLL is the angular frequency measured by the phase-locked loop, ω b is the grid angular frequency.

3. The method for modeling a doubly-fed wind turbine based on a full electromagnetic transient simulation platform according to claim 3 is characterized in that: The shaft system model described in step 1 models the wind turbine, gearbox and generator rotor as three mass blocks. The dynamic equation of the three-mass block model is: Among them, H t , H h , H r Denote the inertia constants of the wind turbine, gearbox and generator concentrated equivalent mass blocks, respectively, D t , D h , D r Denote the damping coefficients of the three mass blocks, D th , D hr They represent the damping coefficients between the wind turbine and the gearbox, and between the gearbox and the generator, respectively. th , K hr are the equivalent stiffness coefficients of the low-speed shaft between the wind turbine and the gearbox, and the high-speed shaft between the gearbox and the generator, respectively. a ,θ b are the torsional angular displacements between the wind turbine and the gearbox, and between the gearbox and the generator, ω t ,ω h ,ω r are the speeds of wind turbine, gearbox and generator respectively, T m , T e They are mechanical torque and electromagnetic torque respectively.

4. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform according to claim 4, characterized in that: In step 4, the generator model uses a two-phase synchronous rotating coordinate system instead of a three-phase stationary coordinate system to decouple and simplify the model, and the generator model includes a stator and rotor voltage equation, a flux equation, and an electromagnetic torque equation; The rotor voltage equation is: Among them, u s and u r are the generator stator and rotor voltages, ψ s and ψ r are the stator and rotor flux of the generator, i s and i r are the stator and rotor currents of the generator respectively; The magnetic flux equation is: Among them, L Is , L Ir are stator and rotor leakage inductance, L m is the mutual inductance between the stator and rotor; The electromagnetic torque equation is: T e =L m (i qs i dr -i ds i qr )。 5. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform according to claim 5, characterized in that: The step 5 is specifically: dividing the grid-side filter into an inductor branch and a capacitor branch, and the inductor branch equation is: Among them, u dg 、u qg is the voltage of the d and q axes output by the grid-side converter, i dg 、i qg is the current of the grid-side filter d and q axes; The capacitor branch equation is: Among them, U d_cl , U q_cl is the d-axis and q-axis components of the voltage across the capacitor, i dl 、i ql are the d-axis and q-axis components of the transmission line inductance current.

6. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform according to claim 6, characterized in that: In step 6, the inverter and its control model include a DC capacitor model, a rotor-side converter control model and a grid-side converter control model; The DC capacitor model is used to maintain the DC capacitor voltage balance, and its equation is: Among them, U dc is the voltage across the DC capacitor; The rotor-side converter control model indirectly adjusts the stator-side output power by controlling the rotor excitation current. The equation is: The grid-side converter control model is used to maintain the stability of the DC bus voltage and realize the control of the AC side power factor. The equation is:

7. A doubly-fed wind turbine modeling method based on a full electromagnetic transient simulation platform according to claim 7, characterized in that: Step 7 is as follows: the transmission line transformer is equivalent to an RL model, and the dynamic equation is: Among them, u d_pcc 、u q_pcc are the voltages of d and q axes at the PCC point respectively.

Images