Energy model building method for interaction between doubly-fed wind power plant units

Abstract

The invention discloses an energy model modeling method for interaction between doubly-fed wind power plant units. And according to the energy flow path of the doubly-fed fan, the energy path of the doubly-fed fan is decomposed into an excitation side energy channel and a network side energy channel. In an excitation side energy channel, after disturbance occurs, disturbance current components pass through a rotor side converter to generate new rotor voltage and stator current, and the newly generated stator current can generate interaction voltage and interaction phase locking angles at other fan ports; in a grid-side energy channel, disturbance current generates disturbance voltage through a grid-side current converter, the disturbance voltage can generate induction current and interaction current on a branch of the disturbance voltage and other branches, and by considering the process, a doubly-fed fan interaction energy equation is constructed. According to the energy model of the doubly-fed wind power plant interaction, the problem that the analysis precision is poor when a traditional model analyzes the wind power integration stability is solved, the stability of a wind power integration system is improved, and the actual engineering requirements are better met.

Description

Technical Field

[0001] The invention relates to modeling technology, and in particular to a method for modeling an energy model of interaction between double-fed wind farm units. Background Art

[0002] With the comprehensive advancement of energy reform, the installed capacity of wind power has gradually increased. On the one hand, wind energy has many advantages such as huge storage capacity, wide distribution, renewable and pollution-free; on the other hand, unlike traditional generators, wind turbines require a large number of power electronic devices to control operating parameters, and the strong time-varying and nonlinear characteristics of power electronic devices make them difficult to control in transient processes, and even cause system oscillations under certain operating conditions. Therefore, it is crucial to explore the factors and trends that affect the stability of wind power grid-connected systems and ensure the stable operation of high-penetration, large-scale wind power grid-connected systems.

[0003] The existing wind power grid-connected system stability analysis methods include: eigenvalue method, complex torque coefficient method, impedance analysis method and dynamic energy analysis method. The basis of the eigenvalue method is to linearize the nonlinear system and solve the eigenvalue of the linearized system, but the problem of "curse of dimensionality" may occur when calculating the characteristic roots of complex high-order systems. The complex torque coefficient method uses the damping torque criterion to analyze the stability of the system. Its research mainly focuses on the analysis of the torque torsional vibration of the wind turbine shaft system, and it is difficult to analyze the interaction between the wind farm and the power grid. The impedance analysis method analyzes the stability of the wind power grid-connected system by depicting the impedance characteristic curve of the wind turbine port and combining the Nyquist stability criterion, but it is difficult to depict the interaction process of oscillation between wind turbines and cannot explain the mechanism of dynamic occurrence and development. The dynamic energy analysis method does not rely on the system equilibrium point, but monitors the occurrence and development of oscillations and evaluates the stability of the wind power grid-connected system by measuring the real-time data of the wind turbine grid connection point.

[0004] At present, most of the research on oscillation of doubly fed wind farms is based on the single-machine equivalent model, ignoring the interaction between the units in the wind farm. The actual operation of the doubly fed wind farm is affected by the geographical location and load conditions, which makes the operating status of each doubly fed wind turbine in the field different. The single-machine equivalent model cannot accurately analyze the dynamic characteristics of each unit in the wind farm during the oscillation process. Therefore, when analyzing the stability of wind power grid connection, the analysis accuracy is poor and may even lead to erroneous results.

[0005] In order to improve the analysis accuracy of the stability of the doubly-fed wind farm grid-connected system, it is necessary to focus on deriving and establishing a mathematical model of the interaction between the doubly-fed wind farm units. Based on the dynamic energy analysis method, the present invention proposes a method for establishing an energy model of the interaction between the doubly-fed wind farm units, and decomposes the interactive energy path into two channels: the excitation side energy channel and the grid side energy channel. By exploring the dynamic development process of transient energy during the oscillation process and depicting the dynamic interaction paths between wind turbines and between wind turbines and the power grid, it has important theoretical significance and practical value for enriching and expanding the oscillation stability analysis and control theory of wind power grid-connected systems and improving the safety and stability level of the system. Summary of the invention

[0006] The purpose of the present invention is to provide an energy modeling method for the interaction between units in a doubly-fed wind farm, to overcome the deficiency of the traditional doubly-fed wind farm aggregation modeling method that cannot reflect the interaction between units, and to improve the safety and stability level of the system.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] An energy modeling method for interaction between doubly-fed wind farm units comprises the following steps:

[0009] Step 1: Establish the traditional energy model of the doubly fed wind turbine, including: establishing the energy model equation of the doubly fed wind turbine in the dq coordinate system, and generalizing it to obtain the energy model of the entire wind farm, dividing the energy of the doubly fed wind turbine into the excitation side energy channel and the grid side energy channel, and establishing its mathematical model equation.

[0010] The traditional energy model of the doubly fed wind turbine in the dq coordinate system is:

[0011]

[0012] Where: is the dynamic energy of the doubly fed wind turbine; Δi d , Δi q , Δu d , Δu q are the dq axis components of the voltage and current at the double-fed wind turbine port; ΔP e represents the active power at the fan port; θ is the angle difference between the dq coordinate system and the xy coordinate system.

[0013] The energy model expression of a single doubly-fed wind turbine port is extended to the entire doubly-fed wind farm. The energy model expression of the entire doubly-fed wind farm is:

[0014]

[0015] In the formula: ΔW farm is the total energy of the doubly-fed wind farm; ΔW DFIG-k is the energy of the kth unit.

[0016] The voltage and current of the doubly fed wind turbine can be expressed by the sum of the voltage and current of the stator side and the grid side ports. The mathematical model equation of the energy channel on the excitation side of the doubly fed wind turbine is:

[0017]

[0018] Where: Δi sdq , Δu sdq are the stator side port current and voltage values ​​of the doubly fed wind turbine.

[0019] The mathematical model equation of the grid-side energy channel of the doubly fed wind turbine is:

[0020] ΔW DFIGg =∫(Δi gd dΔu gq -Δi gq dΔu gd )+ΔP g dΔθ

[0021] Where: Δi gdq , Δu gdq are the current and voltage values ​​of the converter ports on the machine side and grid side of the doubly fed wind turbine.

[0022] Step 2: Establish the energy model of the energy channel on the excitation side of the doubly fed wind turbine and its control system, including: equations considering the interactive voltage and phase-locking angle, the mathematical model of the rotor-side converter, the rotor voltage equation of the doubly fed wind turbine, the stator disturbance current component equation, the stator-side port interactive voltage equation, and the interactive phase-locking angle equation.

[0023] When the system is disturbed, the voltage, current and phase-locking angle of the kth unit are affected by other units in the wind farm. The voltage and phase-locking angle equations considering the interaction are:

[0024]

[0025] Where: Δθ kk , Δu dqkk are the phase-locking angle and voltage dq-axis components generated by the interaction between DFIG-kth and the power grid, recorded as self-locking phase angle and self-voltage components; Δθ km , Δu dqkm are the phase-locking angles generated by DFIG-mth at the DFIG-kth port

[0026] And the voltage dq axis components are recorded as interlocking phase angle and mutual voltage components.

[0027] The control equation of the rotor side converter is:

[0028]

[0029] Where: and represents the proportional and integral parameters of the outer loop control of the converter on the rotor side of the kth wind turbine; and represents the proportional and integral parameters of the inner loop control of the current of the k-th wind turbine rotor side converter; L r is the rotor inductance, L s is the stator inductance, L m is the stator-rotor mutual inductance; ω n =ω s -ω r ,ω r is the rotor speed.

[0030] The voltage equation of the rotor side of the doubly fed wind turbine generator is:

[0031]

[0032] Where: Δu rdk , Δu rqk , Δi rdk , Δi rqk represents the voltage and current on the rotor side of the kth fan, R r Indicates the rotor resistance.

[0033] After the disturbance occurs, the disturbance current passes through the control link of the rotor-side converter, generating a new rotor voltage change, and then passes through the induction generator to generate a new disturbance current component on the stator side. The equation of the stator current disturbance component is:

[0034]

[0035] Where: Δi sdqk0 is the initial current when DFIG-kth is disturbed; Δi sdqk1 It is the stator current newly generated by DFIG-kth through the rotor side control link.

[0036] The stator current newly generated by the mth doubly fed wind turbine generates an alternating voltage component at the port of the kth doubly fed wind turbine. The alternating voltage equation at the stator side port is:

[0037]

[0038] Where: Δu dkm , Δu qkm is the dq-axis component of the alternating voltage variation generated by the mth wind turbine at the kth wind turbine port, Δi dm1 , Δi qm1 is the dq axis component of the disturbance current after the synchronous oscillation of the mth wind turbine, L kis the inductance value between the kth wind turbine and the PCC point, which is expressed as the grid-connected distance of the kth wind turbine, R is the equivalent resistance of the transmission line, L is the equivalent inductance of the transmission line, and C is the series compensation capacitor of the transmission line.

[0039] After the stator-side port interactive voltage passes through the phase-locked loop control link, it will cause the phase-locked angle to change. The equation of the interactive phase-locked angle is:

[0040]

[0041]

[0042] Where: Proportional and integral parameters of the phase-locked loop control link of the DFIG-k fan.

[0043] Step 3: Establish the grid-side energy channel energy model of the doubly-fed wind turbine and its control system, including: establishing the control equation of the grid-side converter of the doubly-fed wind turbine, and establishing the induced current and interaction current equations, and the grid-side converter port voltage and current equations based on the induced voltage and current characteristics.

[0044] The control equation of the grid-side converter of the doubly fed wind turbine is:

[0045]

[0046] Where: Δu gdqk is the voltage change value of the grid-side converter port when subsynchronous oscillation occurs, Δi gdqk is the change in the dq axis component of the grid-side current, K p_g , K i_g are the proportional and integral parameters of the inner loop of the grid-side converter current, L g is the output reactance of the grid-side converter.

[0047] The induced voltage increment Δu of each unit gdk , Δu gqk An induced current will be generated in its own branch. Taking the branch where the kth fan is located as an example to solve the induced current, the induced current equation is:

[0048]

[0049] Where: m kk is the inductance coefficient of the kth fan itself, L kk is the equivalent inductance of the kth wind turbine, which is numerically equal to the sum of the grid-connected inductance of the kth wind turbine and the inductance of other branches in parallel, that is, L N+1 is the equivalent inductance of the transmission line.

[0050] The induced voltage of each unit will also generate induced current in other branches, which is called the alternating current Δi gkm , taking the interactive current generated by the induced voltage of the kth fan in the branch where the mth fan is located as an example, the interactive current equation is:

[0051]

[0052] Where: L k , L m It is represented by the grid connection distance between the kth wind turbine and the mth wind turbine; m km is the interaction coefficient between the kth fan and the mth fan,

[0053] Considering the generation and iteration process of induced voltage, induced current and interactive current, the voltage and current equations of the grid-side converter port are:

[0054]

[0055] Where: The superscript j indicates the jth iteration process.

[0056] Step 4: Combine the equations of steps 1 to 3 to establish an energy model for the interaction between the units in the doubly-fed wind farm, including: establishing the energy channel interaction equation on the excitation side and the energy channel interaction equation on the grid side.

[0057] Combining the equations from step 1 to step 2, we get the interaction equation of the energy channel on the excitation side:

[0058]

[0059] In the formula: ΔW kmr It is the energy generated in the energy channel on the excitation side due to the interaction between the kth unit and the mth unit.

[0060] Combining the equations of step 1 and step 3, we get the grid-side energy channel interaction equation:

[0061]

[0062] In the formula: ΔW kmg It is the energy generated in the grid-side energy channel due to the interaction between the kth unit and the mth unit.

[0063] It can be obtained that the energy model of the interaction between units in the doubly fed wind farm is:

[0064]

[0065] Compared with the existing technology, this technology has the following beneficial effects:

[0066] The present invention comprehensively considers the characteristics of the doubly-fed wind turbine and establishes a capacity model for the interaction between doubly-fed wind farm units, including the excitation side energy channel and the grid side energy channel. During the model establishment process, each physical quantity is clearly defined, the expression is clear, and it has good accuracy. It can be combined with the traditional doubly-fed power plant energy model to form a more comprehensive and more accurate doubly-fed power plant grid-connected system energy model. The present invention provides a model for the parameter design and stability analysis of the doubly-fed power plant grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is the structure diagram of the grid-connected system of the double-fed wind farm;

[0068] Figure 2 A flowchart of a method for establishing an energy model for the interaction between units in a doubly-fed wind farm;

[0069] Figure 3 This is the control block diagram of the rotor-side converter of the doubly-fed wind turbine;

[0070] Figure 4 This is the control block diagram of the grid-side converter of the doubly-fed wind turbine;

[0071] Figure 5(a) is the energy waveform calculated using the traditional energy model of the doubly-fed wind turbine when the system undergoes subsynchronous oscillation;

[0072] Figure 5(b) is the interactive energy waveform of the excitation side channel of the doubly fed wind turbine when the system undergoes subsynchronous oscillation;

[0073] Figure 5(c) is the waveform of the interactive energy in the grid-side channel of the doubly fed wind turbine when the system undergoes subsynchronous oscillation;

[0074] Figure 5(d) is a comparison of the energy waveforms calculated using the traditional energy model of the doubly fed wind turbine and the energy model considering interaction when subsynchronous oscillation occurs in the system. DETAILED DESCRIPTION

[0075] In order to describe the present invention in more detail, the above-mentioned method for establishing the interaction energy model between the units in the doubly-fed wind farm is verified below in combination with the accompanying drawings and specific implementation examples.

[0076] In the PSCAD / ETDMC simulation software, a double-fed wind farm grid-connected system is built, in which the double-fed wind farm is connected to the infinite power grid through the series compensation line, as shown in the figure. Four double-fed wind turbines are connected to the collection bus through a 0.69 / 35kV transformer, and then connected to the infinite system through a 35 / 220kV transformer. The main parameters of the double-fed wind farm are shown in Table 1.

[0077] Table 1

[0078]

[0079] The model starts at 0s and runs stably until 2s, when disturbance is added to make the system produce subsynchronous oscillation. The voltage and current components at the PCC point of each wind turbine are taken respectively, and the energy model establishment method of the interaction between the units of the doubly fed wind farm proposed above is applied to calculate the dynamic energy of each part of the doubly fed wind farm when the subsynchronous oscillation occurs, as shown in Figure 5. It can be seen that when the interaction between the units is considered, the total energy of the wind farm shows a gradual increasing trend, indicating that the subsynchronous oscillation of the system is in a divergent state. When the interaction between the units is not considered, the energy of the system gradually tends to be stable, indicating that the system is in a state of equal amplitude oscillation. In summary, compared with the traditional energy model, the energy model that considers the interaction between the units will obtain more accurate results in stability analysis and is not prone to misjudgment.

[0080] The present invention proposes a method for establishing an energy model of the interaction between units in a doubly-fed wind farm. According to the energy flow path, the interaction energy is decomposed into the excitation side energy channel and the grid side energy channel, respectively. The energy expression of the interaction between the units is constructed by the changes in the voltage, current and phase-locking angle of the stator side port and the grid side port when the disturbance occurs. The interaction between the units is analyzed from the energy perspective, which does not rely on the balance point of the system, but monitors the occurrence and development of oscillation by measuring the real-time data of the wind turbine grid connection point, overcomes the problem that the traditional doubly-fed wind farm mathematical model is difficult to analyze the interaction within the wind farm, avoids the situation that the stability judgment of the wind farm grid-connected operation system based on the mathematical model is wrong, improves the accuracy of the stability judgment, and provides a theoretical basis for the suppression of subsynchronous oscillations of the wind farm grid-connected system, which is more in line with the actual requirements of the project. Finally, it should be noted that the above implementation cases are only used to illustrate the technical solution of the present invention rather than to limit it, but the protection scope of the present invention is not limited thereto. Any technician in the relevant field can still modify or replace the specific implementation of the present invention with the same, which should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for establishing an energy model for the interaction between doubly-fed wind farm units. It is characterized in that The following steps are involved: Step 1: Establish the traditional energy model of the doubly-fed wind turbine; Step 2: Establish the energy model of the energy channel on the excitation side of the doubly-fed wind turbine and its control system; Step 3: Establish the grid-side energy channel energy model of the double-fed wind turbine and its control system; Step 4: Combine the equations from steps 1 to 3 to establish an energy model for the interaction between the units in the doubly fed wind farm.

2. A method for establishing an energy model of interaction between doubly-fed wind farm units according to claim 1, It is characterized in that The step 1: establishing a traditional energy model of a doubly fed wind turbine specifically includes: establishing an energy model equation of the doubly fed wind turbine in a dq coordinate system, and generalizing the energy model of the entire wind farm. The voltage and current of the doubly fed wind turbine can be represented by the sum of the voltage and current of the stator side port and the grid side port. Therefore, the energy of the doubly fed wind turbine is divided into an excitation side energy channel and a grid side energy channel, and its mathematical model equation is established.

3. The method for establishing an energy model of the interaction between doubly-fed wind farm units according to claim 1, It is characterized in that The step 2: establishing an energy model of the energy channel on the excitation side of the doubly-fed wind turbine and its control system, specifically including: establishing voltage and phase-locking angle equations that take into account the interaction, establishing a rotor-side converter mathematical model and a doubly-fed wind turbine rotor voltage equation based on the control structure of the rotor-side converter, establishing an equation for the rotor voltage disturbance component generated when the system is disturbed, and generating an additional disturbance current component equation on the stator side through the induction generator, establishing a stator-side port interaction voltage equation, and an interaction phase-locking angle equation.

4. The method for establishing an energy model of interaction between doubly-fed wind farm units according to claim 1, It is characterized in that The step 3: establishing a grid-side energy channel energy model of the doubly-fed wind turbine and its control system, specifically includes: establishing a control equation for the grid-side converter of the doubly-fed wind turbine, and establishing an induced current and interaction current equation, and a grid-side converter port voltage and current equation based on the induced voltage and current characteristics.

5. The method for establishing an energy model of interaction between doubly-fed wind farm units according to claim 1, It is characterized in that Step 4: Establish an energy model for the interaction between units in a doubly fed wind farm, specifically including: combining the energy mathematical models of the excitation side and grid side energy channels established in step 1, the stator side port interaction voltage equation and the interaction phase-locking angle equation established in step 2, and the grid side port voltage and current equations established in step 3, and respectively obtaining the energy channel interaction equation on the excitation side of the doubly fed wind turbine generator, the grid side energy channel interaction equation, and the total interaction energy equation.

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