CN117613997A - Method and system for analyzing output power oscillation characteristics of doubly-fed wind turbine generator of micro-grid - Google Patents
Method and system for analyzing output power oscillation characteristics of doubly-fed wind turbine generator of micro-grid Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
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Abstract
The invention discloses a method and a system for analyzing the oscillation characteristics of output power of a doubly-fed wind turbine generator of a micro-grid. And if any one device in the micro-grid oscillates, the output non-power frequency signal of the device is coupled with other devices, so that the oscillation propagates in the micro-grid and the operation of the grid is affected. In order to study coupling and oscillation characteristics among power equipment in a micro-grid, the oscillation characteristics of each equipment are studied firstly, and energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine are deduced based on a transient energy flow method, a wind speed and a turbine control strategy aiming at the doubly-fed wind turbine; then, researching the change mechanism of energy consumption of each subsystem when the running parameters such as wind speed, unit control parameters and the like are changed, and analyzing the oscillation characteristics of the unit; finally, modeling simulation is carried out on the PSCAD/EMTDC platform, and the rationality of the method is verified.
Description
Technical Field
The invention relates to a method and a system for analyzing the oscillation characteristics of output power of a doubly-fed wind turbine generator of a micro-grid.
Background
The micro-grid is a small power system which covers new energy distributed power generation, energy storage and load such as wind power generation, photovoltaic power generation and the like. The AC/DC hybrid micro-grid interface is flexible, has the characteristic of friendly acceptance of distributed power and load, can fully exert the respective power supply advantages of an AC/DC system, and is a long-term existing form and an important development direction of the micro-grid.
Each distributed power supply and load in the micro-grid are tightly connected and coupled with each other through an alternating current-direct current network; and the micro-grid has the characteristics of limited capacity, small inertia and low inertia weak damping. If any one device in the micro-grid oscillates, an oscillation signal in the output power of the device is applied to other devices to become a forced disturbance source, so that other original units which normally operate oscillate, and the oscillation propagates in the micro-grid to influence the operation of the micro-grid. It is therefore important to study the oscillation characteristics of the individual devices in the micro-grid and analyze their interactions in order to find the oscillation source in time, determine the propagation path of the oscillation, and take effective measures to calm the oscillation at the beginning of the oscillation.
In the research of the oscillation characteristics of the wind turbine generator, the methods commonly adopted at present include a frequency scanning method, a time domain simulation method, a complex torque coefficient method, a eigenvalue analysis method, an impedance analysis method, an open-loop mode method, a transient energy function method and the like. The transient energy function method not only evaluates the damping of the wind turbine generator set from the angle of energy, but also researches the influence of different parameters on system oscillation; the method can also be used for positioning an oscillation source of a power system, and is widely applied to the stability research of a micro-grid.
In the current research, an energy function is established by considering a doubly-fed wind turbine control system model and parameters, the influence of the change of control parameters on energy consumption and damping of the doubly-fed wind turbine is studied in detail, and the oscillation characteristic of the output power of the doubly-fed wind turbine is analyzed, but the change of wind speed is not considered. Since wind speed varies randomly, and the wind turbine control strategy is dependent on wind speed.
The wind turbine generator system has a plurality of reasons for oscillation, such as the wind turbine generator system oscillates when a short circuit fault occurs in the system or the system suffers from large disturbance, and energy functions of the doubly-fed wind turbine generator system and the direct-drive permanent magnet wind turbine generator system are established from the angle of a power grid in the literature, so that damping characteristics of the wind turbine generator system and influence of the damping characteristics on the oscillation characteristics of the system are researched; in addition, the improper setting of control parameters of the wind turbine can weaken the damping of the wind turbine and spontaneously oscillate, so that the operation of other turbines in the micro-grid is further affected; in addition, the wind speed is used as a random disturbance source of the wind turbine generator and is coupled with a control system of the wind turbine generator, so that the operation characteristics of the wind turbine generator are further affected.
In summary, changes in the wind speed, the unit control parameters, and other operating parameters need to be considered simultaneously in order to analyze the oscillation characteristics of the unit.
Disclosure of Invention
The invention aims to provide a method for analyzing the oscillation characteristics of the output power of a doubly-fed wind turbine generator of a micro-grid, which fully considers the changes of running parameters such as wind speed, control parameters of the generator and the like so as to analyze the oscillation characteristics of the generator.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the method for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator of the micro-grid comprises the following steps:
step 1, based on a transient energy flow method, a wind speed and a unit control strategy are calculated, and energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator are deduced;
and 2, analyzing the change mechanism of energy consumption of each subsystem when the wind speed and the unit control parameters are changed based on the energy functions of the wind turbine subsystem, the generator and the excitation subsystem constructed in the step 1, so as to obtain the unit oscillation characteristics.
In addition, on the basis of the analysis method of the oscillation characteristics of the output power of the micro-grid double-fed wind turbine, the invention also provides a micro-grid double-fed wind turbine oscillation characteristic analysis system which is adaptive to the analysis method, and the analysis method adopts the following technical scheme:
an output power oscillation characteristic analysis system of a micro-grid double-fed wind turbine generator system, comprising:
the energy function calculation module is used for calculating an energy function of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator based on a transient energy flow method, a wind speed and a unit control strategy; and the unit oscillation characteristic analysis module is used for analyzing the wind speed and the change mechanism of the energy consumption of each subsystem when the unit control parameters are changed based on the constructed energy functions of the wind turbine subsystem, the generator and the excitation subsystem, so as to obtain the unit oscillation characteristic.
The invention has the following advantages:
as described above, the invention relates to a method and a system for analyzing the oscillation characteristics of the output power of a doubly-fed wind turbine generator of a micro-grid. Aiming at the doubly-fed wind turbine, the energy functions of a wind turbine subsystem, a generator and an excitation subsystem are deduced according to wind speed change and a turbine control strategy; and then, researching the influence mechanism of the running parameter changes such as wind speed, control parameters and the like on the energy consumption of a wind turbine subsystem, a generator and an excitation subsystem in the micro-grid, and analyzing the influence of the wind speed and unit control parameters on the output power oscillation characteristics of the doubly-fed wind turbine. Because the method fully considers the changes of the running parameters such as wind speed, unit control parameters and the like, the oscillation characteristics of the unit are convenient to analyze, compared with the defects that the traditional analysis method generally needs detailed model parameters or a large amount of measurement data, the application range is limited and the positioning process is complex, the transient energy flow method adopted by the method can analyze from the angle of energy, does not depend on a specific model, is easy to obtain calculated variables and has wide application range.
Drawings
Fig. 1 is a flowchart of a method for analyzing output power oscillation characteristics of a doubly-fed wind turbine generator of a micro-grid in an embodiment of the invention.
Fig. 2 is a schematic diagram of a grid-connected system of a doubly-fed wind turbine in an embodiment of the invention.
Fig. 3 is a schematic diagram of the power flow when the control parameters of the converter are changed in the simulation experiment according to the present invention.
FIG. 4 is a schematic diagram of damping ratio and eigenvalue during normal operation of the unit in the simulation experiment of the present invention.
FIG. 5 is a schematic diagram of damping ratio and characteristic value of the unit in weak damping in the simulation experiment of the invention.
FIG. 6 is a diagram showing damping ratio and eigenvalue of the unit during negative damping in the simulation experiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and detailed description:
example 1
And if any one device in the micro-grid oscillates, the output non-power frequency signal of the device is coupled with other devices, so that the oscillation propagates in the micro-grid and the operation of the grid is affected. In order to study the coupling and oscillation characteristics among power equipment in a micro-grid, the oscillation characteristics of each equipment are studied firstly, therefore, the invention provides a micro-grid double-fed wind turbine generator output power oscillation characteristic analysis method which considers the changes of running parameters such as wind speed, unit control parameters and the like, and the method aims at a double-fed wind turbine generator to calculate the wind speed and unit control strategy based on a transient energy flow method and deduce energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the double-fed wind turbine generator; then, researching the change mechanism of energy consumption of each subsystem when the running parameters such as wind speed, unit control parameters and the like are changed, and analyzing the oscillation characteristics of the unit; and finally, modeling and simulating the PSCAD/EMTDC platform, analyzing the energy change and the power oscillation characteristic of the doubly-fed wind turbine generator when the operation parameters change, comparing the energy change and the power oscillation characteristic with a characteristic value calculation result, and verifying the rationality of the analysis.
As shown in FIG. 1, the method for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator of the micro-grid comprises the following steps:
and step 1, based on a transient energy flow method, a wind speed and a unit control strategy are calculated, and energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator are deduced.
The energy flow composition of the doubly-fed wind turbine is shown in FIG. 2. The total energy flow W of the unit comprises W 1 And W is 2 The method comprises the steps of carrying out a first treatment on the surface of the Wherein W is 1 By wind turbine subsystem energy flow W 11 And generator and excitation subsystem energy flow W 12 Constructing; w (W) 2 Is the transient energy of the grid-side converter. Taking the energy emitted by the double-fed wind turbine generator as a positive reference direction, the energy functions of all subsystems of the double-fed wind turbine generator are as follows:
W＝ W 1 +W 2 ＝ W 11 + W 12 + W 2 (1)
wherein K is wg The rigidity coefficient of the shafting is; h w And H g Inertial time constants of the wind turbine and the generator; t (T) w Is the torque of the wind turbine; delta w And delta g For the electrical angular displacement of wind turbines and generators, and delta wg ＝δ w -δ g 。D ww 、D gg And D wg The self damping coefficients of the wind turbine and the generator and the mutual damping coefficient between the wind turbine and the generator are respectively; u (u) gd 、u gq 、i gd 、i gq D and q axis components of the grid side voltage and current, respectively; omega 0 Represents synchronous rotational speed omega w Indicating the rotating speed omega of the wind turbine g Indicating the generator speed. X is X m To excite reactance, X s For stator synchronous reactance.
Due to transient energy W of the grid-side converter 2 There is no integral term in the following, the energy functions of the wind turbine subsystem, the generator and the excitation subsystem are analyzed with emphasis. In the energy function formula, the wind speed is considered to be kept unchanged, energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator are further deduced by considering the wind speed change, and the energy change and the unit output power of each subsystem are analyzed when the wind speed changes.
When the wind speed is smaller than the rated wind speed of the unit, the wind turbine adopts a control strategy of maximum power tracking control to ensure that the wind turbine runs at the optimal power, a wind turbine control system and a converter control are mutually coupled, and a formula (2) is further deduced to obtain W 11 The method comprises the following steps:
wherein σ represents the slip;i sd i is the d-axis component of the stator current rd 、i rq Respectively the dq-axis component, K of the rotor current p 、K i The current transformer inner ring proportional coefficient and the integral coefficient.
When the wind speed is greater than the rated wind speed of the unit, the wind turbine adopts pitch angle control to enable the unit to operate in a rated state, and then W 11 The method comprises the following steps:
wherein ρ is air density, and R is wind wheel radius; v is the basic wind speed; k is the power coefficient.
Wind turbine subsystem energy flow W 11 Comprises the rotating speed omega of the wind turbine w Rotational speed omega of generator g Slip sigma and wind speed V; when the wind speed changes, the components change with each other, W 11 The components of the intermediate integral related to the path also change.
According to the mathematical model of the doubly-fed wind turbine, the energy flow W of the generator and the excitation subsystem is obtained through deduction 12 ：
Wherein u is rd 、u rq Respectively the dq-axis component of the rotor voltage, R r Is rotor resistance; i.e sq Representing the q-axis component, e ', of the stator current' d Representation and e' q Representing dq-axis components, X, of respectively transient voltage sources r Is the rotor loop reactance.
e′ q1 、e′ d1 The expression of (2) is as follows:
the first two conservation items in the formula (7) which are irrelevant to the integral path represent the change of transient energy of the generator and the excitation subsystem; the third to seventh terms are non-conservative terms related to the integration path, representing the energy consumption of the generator and the excitation subsystem; wherein the fifth to seventh terms relate to the unit slip sigma, and the last term relates to sigma 2 Related to the following. In the energy functional formulas (5 and 6) of the wind turbine subsystem and the energy functional formula (7) of the generator and the excitation subsystem, the component related to the integral path is energy consumed by the unit, namely dissipation energy, and reflects the damping characteristic of the unit. If the element damping is positive, the element consumes energy; if the element damping is negative, the element emits energy (defining the unit emitting energy as positive). The change in energy consumed by the element is expressed in terms of energy flow power.
Generator and excitation subsystem energy flow W 12 The calculation process of (2) is as follows:
the voltage and flux linkage equations of a doubly fed induction generator are expressed in the rotating dq0 coordinate system as:
wherein u is sd 、u sq Respectively dq axis components of the stator voltage; r is R s 、R r The resistances of the stator and the rotor are respectively; l (L) s 、L r The self-inductance of the stator and the rotor respectively; l (L) m Is the mutual inductance between the stator and the rotor.
Using a transient power supply e=e' d +je′ q The three-order simplified model of the doubly-fed induction motor is characterized by comprising the following steps:
in the above, X' =x s +X r ||X m X' is the transient reactance. Substituting formula (8) into formula (9) to obtain:
in the above, de' d /dt、de′ q Dividing dt into two parts including no slip and slip; substituting the formulas (8) and (10) into the formula (5) to simplify the formula to obtain the energy flow W of the generator and the excitation subsystem 12 I.e., equation (7).
And 2, analyzing the change mechanism of energy consumption of each subsystem when the wind speed and the unit control parameters are changed based on the energy functions of the wind turbine subsystem, the generator and the excitation subsystem constructed in the step 1, so as to obtain the unit oscillation characteristics.
From the energy functions (5) to (7) of the doubly-fed wind turbine generator, the energy functions of the wind turbine subsystem, the generator and the excitation subsystem are related to the input wind speed, mechanical, electrical, control and other operation parameters of the doubly-fed wind turbine generator. Wherein the mechanical, electrical and control parameters determine the damping of the unit itself, whereas the wind speed is a randomly varying external disturbance. When the wind speed is smaller than or greater than the rated wind speed of the unit, the control strategies of the doubly-fed wind turbine unit are different, and energy functions of wind turbine subsystems in the unit are different, so that the influence of wind speed change on subsynchronous oscillation of the unit is researched under the two conditions that the wind speed is smaller than or greater than the rated wind speed of the unit.
When the wind speed is smaller than the rated wind speed of the unit, the influence of the wind speed change on subsynchronous oscillation of the unit is as follows:
when the doubly-fed wind turbine generator runs normally at rated wind speed, the rotating speed omega of the wind turbine w And generator speed omega g The slip sigma is increased along with the increase of the wind speed, and the slip sigma is reduced along with the increase of the wind speed; in the formula (5), the energy consumed by the shafting of the unit isThey increase as the wind speed increases; meanwhile, when the wind speed is increased, the slip sigma is reduced, the (1-sigma) is increased, and the consumption energy of a maximum power tracking control system of the wind turbine is increased, so that the damping of a subsystem of the wind turbine is increased along with the increase of the wind speed; in equation (7), the energy consumption related to the integration path is the unit slip σ, σ 2 And thus W 12 The energy consumption of the generator and the excitation subsystem is reduced along with the increase of the wind speed, and the damping of the generator and the excitation subsystem is weakened along with the increase of the wind speed.
The energy consumed by the doubly-fed wind turbine generator is determined by the energy consumed by the wind turbine subsystem, the generator and the excitation subsystem, and the trend of the energy consumed by the wind turbine subsystem, the generator and the excitation subsystem along with the change of wind speed is opposite; because the damping coefficient of the shafting of the unit is larger than 1,0 < sigma < 1, and W 12 The seventh term of (2) and the slip square sigma 2 In relation, therefore, the wind speed variation has less influence on the energy consumption of the generator and the excitation subsystem than the wind turbine subsystem; wind speed increaseThe energy consumption of the wind turbine subsystem is increased by an amount larger than the energy consumption of the generator and the excitation subsystem; the doubly-fed wind turbine generator runs below the rated wind speed, and the energy consumed by the doubly-fed wind turbine generator when the wind speed changes is determined by the wind turbine subsystem and is reduced along with the reduction of the wind speed.
When the electric and control parameters of the doubly-fed wind turbine are set reasonably, and the damping of the doubly-fed wind turbine is strong enough, the energy consumed by the doubly-fed wind turbine can still keep normal operation even though the energy consumed by the doubly-fed wind turbine is reduced along with the reduction of the wind speed; if the control parameters of the unit converter are improperly set, the unit damping is weakened but still positive damping is achieved, and the unit consumes less energy; when the wind speed is reduced, the energy consumed by the unit is further reduced, and the unit changes from consumed energy to output energy, so that the unit oscillates; if the control parameters of the unit converter are set improperly, the unit is negative damped and subsynchronous oscillation occurs, and then the unit outputs energy; because the energy consumed by the unit is reduced along with the reduction of the wind speed, the output energy of the unit is increased along with the reduction of the wind speed, so that the reduction of the wind speed aggravates the original subsynchronous oscillation of the unit, the amplitude of the output power is increased along with the reduction of the wind speed, and the oscillation frequency drifts along with the change of the wind speed.
When the wind speed is smaller than the rated wind speed of the unit, the influence of the wind speed change on subsynchronous oscillation of the unit is as follows:
as seen from equation (6), the energy consumed by the wind turbine subsystem is related to the energy consumed by the shafting damping and the energy consumed by the wind turbine impeller; compared with the wind speed which is smaller than the rated wind speed of the unit, the energy consumed by the subsystem of the wind turbine is larger at the moment; when the input wind speed of the wind turbine is rated, the slip ratio of the wind turbine is approaching zero, i.e. sigma is approximately equal to 0, and the energy W of the generator and the excitation subsystem is equal to the energy W of the excitation subsystem 12 The fifth through seventh terms are equal to 0, and therefore, the generator and excitation subsystem will consume less energy at this time than if the wind speed were less than the rated wind speed of the unit.
When the input wind speed of the wind turbine is greater than the rated wind speed of the unit, the wind turbine enables the unit to operate in a rated state through pitch angle control, and the slip ratio sigma is approximately equal to 0, so that W is obtained 11 And W is 12 And does not change with the input wind speed; the double-fed wind turbine generator runs above the rated wind speed,the energy consumed by the set when the wind speed changes is determined by the wind turbine subsystem and does not change along with the change of the wind speed; therefore, under various damping states of the doubly-fed wind turbine generator, the wind speed change does not influence the oscillation characteristics of the output power of the generator.
In addition, in order to verify the effectiveness of the oscillation characteristic analysis method provided by the invention, the following simulation verification process is also provided.
And (3) constructing a grid-connected system model of the doubly-fed wind turbine shown in the figure 2 in the PSCAD/EMTDC, and comparing the energy change of the wind turbine and the oscillation characteristic of the output power with the analysis result of the system eigenvalue when the running parameters such as wind speed, control parameters and the like are changed through the transient energy flow method simulation analysis. The doubly-fed wind turbine generator is connected with an infinite system through a 0.69kV/35kV outlet transformer and a 35kV/220kV step-up transformer, and rated wind speed is 11.4m/s.
When the wind speed is smaller than the rated wind speed of the unit, in the doubly-fed wind turbine unit, the scaling factor K of the inner ring control link of the rotor-side converter p And integral coefficient K i The damping effect on the unit is large; set damping following inner ring proportionality coefficient K p Increase or integrate coefficient K i Decreasing and weakening, the power of the energy flow changes from negative to positive. Wind speed of 7m/s, K is changed p 、K i The simulation results in the energy flow power of the unit shown in figure 3. If K p =0.0828, then K i When=0.337, the unit energy flow power is 0. Below hold K p =0.0828 unchanged, change K i The damping of the unit is changed by numerical value, and simulation analysis is carried out by combining the wind speed change.
When the unit normally operates and the damping is strong, the control parameter K of the inner ring of the converter p ＝0.0828，K i =0.85, the input wind speed is 7m/s. And calculating the characteristic value of the grid-connected system of the double-fed wind turbine to obtain the characteristic value, the oscillation mode and the damping ratio shown in table 1.
TABLE 1 eigenvalues during normal operation of the unit
As can be seen from Table 1, the real part of the characteristic root of the unit is always on the left half plane of the coordinate, the damping ratio is positive, and the unit operates normally. When the wind speed changes, the real part of the characteristic value of the mode 3 decreases along with the change of the wind speed, the damping ratio increases along with the increase of the wind speed, and the changing curve is shown in fig. 4; while the real part of the characteristic value of other modes is almost unchanged when the wind speed changes. Therefore, the change rule of the characteristic value and the damping ratio of the wind speed change time group is analyzed in a mode 3. Simulation calculation is carried out on the system in fig. 2, so that energy consumption of a wind turbine subsystem, a generator, an excitation subsystem and the double-fed wind turbine generator is shown in fig. 5, and energy flow power is shown in table 2.
TABLE 2 energy flow Power during normal operation of the Unit
As can be seen from table 2, the wind turbine subsystem consumes energy increasing with increasing wind speed and the power of the energy flow decreases with increasing wind speed; the energy consumed by the generator and the excitation subsystem decreases with increasing wind speed, and the energy flow power increases with increasing wind speed. When the wind speed changes the same, the energy consumption of the wind turbine subsystem is increased more than the energy consumption of the generator and the excitation subsystem, for example, the wind speed is increased from 4m/s to 5m/s, the energy consumption of the wind turbine subsystem is increased by 0.1172pu when the energy flow power is reduced by 0.0266pu and the energy consumption of the generator and the excitation subsystem is reduced by 0.0097pu when the energy flow power is increased by t=5s, and the energy consumption is reduced by 0.049pu. Therefore, when the wind speed changes, the energy consumption of the doubly-fed wind turbine generator is mainly determined by the wind turbine subsystem and increases along with the increase of the wind speed. As shown in Table 2, the energy flow power of the doubly-fed wind turbine generator is reduced along with the increase of the wind speed, and the damping of the doubly-fed wind turbine generator is enhanced. The correctness and rationality of the energy function are further verified in the same way as the conclusion of FIG. 4 is obtained by analyzing the damping characteristics of the unit by utilizing the characteristic values. And performing time domain simulation on the unit to obtain the output active power and current of the doubly-fed wind turbine generator when the wind speed changes, wherein the output power of the unit is stable, the current output waveform has no obvious fluctuation, and the unit is in a stable state.
When the damping of the unit is weaker, the wind speed is 7m/s, and the inner ring proportion coefficient K of the rotor-side converter is maintained p =0.0828 unchanged, decreasing the integral coefficient, K i =0.352, and the result of the eigenvalue calculation is shown in table 3.
TABLE 3 eigenvalues during set weak damping
In general, the unit damping ratio is less than 0.05, and the damping is considered relatively weak. As can be seen from Table 3, after changing the control parameters, the damping ratio of mode 3 is 0.047, which is less than 0.05, and the unit operates in a weak damping state. The wind speed is changed and eigenvalue calculations are performed, mode 3 eigenvalue real part and damping such as shown in fig. 5. As can be seen from the graph, when the wind speed is 4-6 m/s, the real part of the characteristic value of the mode 3 is positive, and the damping of the unit is negative; when the wind speed is greater than 7m/s, the real part of the characteristic value is changed from a positive value to a negative value, and the damping ratio is changed from a negative value to a positive value. When the wind speed changes, the energy flow power of the unit is shown in table 4.
TABLE 4 energy flow power during weak damping of units
From Table 4, it is found that when the wind speed is 7m/s, the energy consumed by the wind turbine subsystem is greater than the energy generated by the generator and the excitation subsystem, the doubly-fed wind turbine generator is still in an energy-consuming operating state, the damping is positive, and the energy flow power is-0.0189, but in a boundary state. Because the energy consumed by the wind turbine subsystem is reduced along with the reduction of the wind speed, when the wind speed is reduced from 7m/s to 6m/s, 5m/s and 4m/s, the doubly-fed wind turbine generator changes from consumed energy to output energy, the energy flow power changes from a negative value to a positive value, and the damping changes from weak damping to negative damping to oscillate. At a wind speed of 7m/s, the unit output clearly has power fluctuations, but the fluctuation amplitude becomes smaller with increasing time. When the wind speed is reduced to 4m/s, the fluctuation of the active power output by the unit is continuously increased to generate oscillation, and the power oscillation frequency is 4.52Hz; when the wind speed rises to 11m/s, the fluctuation amplitude of the active power output by the unit is small, the unit operates normally, and the power oscillation frequency is 7.14Hz. Because the energy consumed by the wind turbine subsystem in the doubly-fed wind turbine generator is reduced as the input wind speed is reduced, subsynchronous oscillations may occur when the doubly-fed wind turbine generator with less damping is operated at low wind speeds.
When the unit damping is negative damping, the wind speed is 7m/s, and the inner ring proportion coefficient K of the rotor-side converter is maintained p =0.0828, further decreasing the integral coefficient, K i The eigenvalue calculation was performed with =0.254, and the results are shown in table 5.
TABLE 5 eigenvalues during negative damping of units
From Table 5, K i When=0.254, the unit oscillation mode 3 damping ratio is negative, i.e. the unit operates in a negative damping state when the wind speed is 7m/s. The wind speed is changed and eigenvalue calculation is performed, and the real part of the eigenvalue and damping of mode 3 are as shown in fig. 6. It can be obtained from the graph that when the wind speed is 4-7.5 m/s, the real part of the characteristic value is positive, and the damping of the unit is negative; when the wind speed is 7.5-11 m/s, the real part of the characteristic value is changed from a positive value to a negative value, and the damping ratio is changed from a negative value to a positive value. When the wind speed changes, the energy flow power of the unit is shown in table 6.
TABLE 6 energy flow power during negative damping of units
As can be seen from Table 6, at a wind speed of 7m/s, the energy flow power of the wind turbine subsystem, the generator and the excitation subsystem and the unit are all positive values, and the unit damping is negative and subsynchronous divergent oscillations are generated. Because the energy consumed by the wind turbine subsystem is reduced along with the reduction of the wind speed, when the wind speed is reduced from 7.5m/s to 4m/s, the output energy of the unit is continuously increased, the energy flow power is gradually increased, and the damping is further reduced; when the wind speed is increased from 7.5m/s to 11m/s, the doubly-fed wind turbine generator is changed from energy emission to energy consumption, the energy flow power is changed from a positive value to a negative value, and the damping is changed from negative damping to positive damping and gradually increased, so that the oscillation subsides. And performing time domain simulation on the grid-connected system of the doubly-fed wind turbine generator to obtain the output current and the spectrogram of the generator when the wind speed changes. When the wind speed is 7m/s, the fluctuation amplitude of the power current is large, and the wind speed is in a slow divergence state. When the wind speed is reduced from 7m/s to 4m/s, the divergence degree of power and current fluctuation is increased, the oscillation amplitude is further increased, and at the moment, the power oscillation frequency is 5.71Hz; when the wind speed is increased from 7m/s to 11m/s, the fluctuation of power and current oscillation is reduced, the oscillation divergence is changed into the oscillation convergence, and the power oscillation frequency is 7.14Hz. From the above analysis, it is seen that when the unit damping is negative, the wind speed increases and the unit stability increases.
When the wind speed is greater than the rated wind speed of the unit, the wind speed is 13m/s and the inner ring of the rotor-side converter of the doubly-fed wind turbine controls the proportionality coefficient K when the unit operates normally and has stronger damping p =0.0828, integral coefficient K i =0.85. And calculating the characteristic value of the grid-connected system of the doubly-fed wind turbine, and obtaining the characteristic value, the oscillation mode and the damping ratio shown in a table 7.
TABLE 7 eigenvalues during normal operation of the unit
As can be seen from the characteristic values, the set stably operates when the wind speed is 13m/s, when the wind speed is 12m/s, 13m/s and 14m/s respectively, the energy flow power of the wind turbine subsystem is-0.2929, -0.293, -0.2929, the energy flow power of the generator and the excitation subsystem is 0.0008, and the energy flow power of the set is-0.2918. As can be seen from simulation results, after the input wind speed exceeds the rated wind speed, the unit maintains the rotating speed of the wind turbine to be near the rated wind speed through pitch angle control. When the wind speed changes, the energy consumption, the energy flow power, the damping ratio, the output power and the current of the unit are all kept unchanged. But the energy consumption of the wind turbine subsystem is far greater than that of the generator and the excitation subsystem, and when the rated wind speed is higher than the rated wind speed, the damping of the doubly-fed wind turbine is mainly determined by the wind turbine subsystem.
When the damping of the unit is weaker, the integral coefficient K of the inner ring of the unit is reduced p ＝0.0828，K i =0.102, the calculated eigenvalues result in:
table 8 eigenvalues during set weak damping
As can be seen from the characteristic values of the wind turbine, when the wind speed is 13m/s, the mode 3 damping ratio is smaller than 0.05, the wind turbine is in a weak damping running state, when the wind speeds are respectively 12m/s, 13m/s and 14m/s, the energy flow power of the wind turbine subsystem is approximately-0.2921, the energy flow power of the generator and the excitation subsystem is-0.2294, -0.2286, -0.2285, and the energy flow power of the wind turbine is-0.065, -0.0657 and-0.0658. Above rated wind speed, when the unit runs in weak damping, the energy consumed by the wind turbine subsystem is greater than the energy emitted by the generator and the excitation subsystem. When the wind speed changes, the energy flow power, the consumed energy, the unit damping ratio and the characteristic value of the wind turbine subsystem, the generator and the excitation subsystem are not basically changed along with the change of the wind speed. The unit output current, power fluctuation, converges with time, and there is 13Hz in power, 37/73Hz subsynchronous component in current. When the wind speed changes, the magnitude of the component is basically the same.
When the unit damping is negative damping, the integral coefficient K of the inner ring of the unit is reduced again p ＝0.0828，K i = 0.09305, computer group eigenvalues:
TABLE 9 eigenvalues during negative damping of units
The result of the calculation of the characteristic value can be obtained, when the wind speed is 13m/s, the damping ratio of the mode 3 is smaller than 0, and at the moment, the unit is in a negative damping running state. When the wind speeds are respectively 12m/s, 13m/s and 14m/s, the energy flow power of the wind turbine subsystem is-0.2918, -0.2922, -0.2917, the energy flow power of the generator and the excitation subsystem is 0.3298, 0.3312 and 0.3321, and the energy flow power of the unit is 0.0483, 0.0494 and 0.0499. When the unit damping is negative, the energy consumed by the wind turbine subsystem is smaller than the energy sent by the generator and the excitation subsystem, so that the total current power of the unit is positive, and the energy is in a divergent state; when the wind speed changes, the energy flow power and the consumed energy of the wind turbine subsystem, the generator and the excitation subsystem are not changed greatly, and the characteristic value and the damping ratio are basically unchanged. The output current and power fluctuation of the unit diverge with the increase of time, the subsynchronous component of 14Hz exists in the power, and the subsynchronous component of 36/74Hz exists in the current, and when the wind speed increases or decreases, the output quantity and the frequency spectrum waveform of the unit still remain unchanged.
Because the control strategies of the doubly-fed wind turbine generator are different when the wind speed is smaller than or greater than the rated wind speed of the generator, and the energy functions of the wind turbine subsystems in the generator are different, the influence mechanism of running parameter changes such as wind speed, control parameters and the like on the energy consumption of the generator and the influence on the oscillation characteristics of the output power of the generator are analyzed. Under the condition that the damping of the doubly-fed wind turbine generator is respectively strong damping, weak damping and negative damping, the wind speed change is considered, and the rule that the energy consumption of the doubly-fed wind turbine generator is reduced along with the reduction of the wind speed is further verified. The rationality of the invention is further verified by a eigenvalue method and time domain simulation. The method comprises the following steps:
1) When the wind speed is smaller than the rated wind speed of the unit, the wind speed and the unit control parameter are coupled to jointly influence the oscillation characteristic of the unit. Because the energy consumed by the unit is reduced along with the reduction of the wind speed, the reduction of the wind speed can lead the damping of the unit to be weakened so as to oscillate or aggravate the original subsynchronous oscillation of the unit, the amplitude of the output power is increased along with the reduction of the wind speed, and the oscillation frequency drifts along with the change of the wind speed.
2) The energy consumption of the doubly-fed wind turbine generator is mainly determined by a wind turbine subsystem when the wind speed changes, so that new knowledge of the wind speed changes on the oscillation influence mechanism of the doubly-fed wind turbine generator is obtained, and the doubly-fed wind turbine generator has guiding significance on the oscillation suppression of the micro-grid.
Example 2
Embodiment 2 describes a system for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator of the micro-grid, which is based on the same inventive concept as the method for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator of the micro-grid in embodiment 1.
An output power oscillation characteristic analysis system of a micro-grid double-fed wind turbine generator system, comprising:
the energy function calculation module is used for calculating an energy function of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator based on a transient energy flow method, a wind speed and a unit control strategy;
and the unit oscillation characteristic analysis module is used for analyzing the wind speed and the change mechanism of the energy consumption of each subsystem when the unit control parameters are changed based on the constructed energy functions of the wind turbine subsystem, the generator and the excitation subsystem, so as to obtain the unit oscillation characteristic.
It should be noted that, in the analysis system of the output power oscillation characteristics of the doubly-fed wind turbine generator system of the micro-grid, the implementation process of the functions and roles of each functional module is specifically shown in the implementation process of the corresponding steps in the method in embodiment 1, and will not be described herein again.
The foregoing description is, of course, merely illustrative of preferred embodiments of the present invention, and it should be understood that the present invention is not limited to the above-described embodiments, but is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Claims (9)
1. A method for analyzing the oscillation characteristics of the output power of a doubly-fed wind turbine generator of a micro-grid is characterized in that,
the method comprises the following steps:
step 1, based on a transient energy flow method, a wind speed and a unit control strategy are calculated, and energy functions of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator are deduced;
and 2, analyzing the change mechanism of energy consumption of each subsystem when the wind speed and the unit control parameters are changed based on the energy functions of the wind turbine subsystem, the generator and the excitation subsystem constructed in the step 1, so as to obtain the unit oscillation characteristics.
2. The method for analyzing the output power oscillation characteristics of the doubly-fed wind turbine generator of the micro-grid according to claim 1, wherein the method comprises the steps of,
the step 1 specifically comprises the following steps:
the total energy flow W of the unit comprises W 1 And W is 2 The method comprises the steps of carrying out a first treatment on the surface of the Wherein W is 1 By wind turbine subsystem energy flow W 11 And generator and excitation subsystem energy flow W 12 Constructing; w (W) 2 Transient energy of the grid-side converter; taking the energy emitted by the double-fed wind turbine generator as a positive reference direction, the energy functions of all subsystems of the double-fed wind turbine generator are as follows:
W＝W 1 +W 2 ＝W 11 +W 12 +W 2 (I)。
3. the method for analyzing the output power oscillation characteristics of the doubly-fed wind turbine generator of the micro-grid according to claim 2, wherein the method comprises the steps of,
in the step 1, the energy flow W of the subsystem of the wind turbine 11 The solving process of (2) is as follows:
when the wind speed is smaller than the rated wind speed of the unit, the wind turbine adopts a control strategy of maximum power tracking control, so that the wind turbine operates at the optimal power, and a wind turbine control system is controlled by a converterMutual coupling of W 11 The method comprises the following steps:
wherein K is wg The rigidity coefficient of the shafting is; h w And H g Inertial time constants of the wind turbine and the generator; t (T) w Is the torque of the wind turbine; delta w And delta g For the electrical angular displacement of wind turbines and generators, and delta wg ＝δ w -δ g ；D ww 、D gg And D wg The self damping coefficients of the wind turbine and the generator and the mutual damping coefficient between the wind turbine and the generator are respectively; omega 0 Represents synchronous rotational speed omega w Indicating the rotating speed omega of the wind turbine g Representing the generator speed; sigma represents slip; x is X m To excite reactance, X s For the synchronous reactance of the stator,i sd i is the d-axis component of the stator current rd 、i rq Respectively the dq-axis component, K of the rotor current p 、K i The current transformer inner ring proportion coefficient and integral coefficient;
when the wind speed is greater than the rated wind speed of the unit, the wind turbine adopts pitch angle control to enable the unit to operate in a rated state, and then W 11 The method comprises the following steps:
wherein ρ is air density, and R is wind wheel radius; v is the basic wind speed; k is the power coefficient.
4. The method for analyzing the output power oscillation characteristics of the doubly-fed wind turbine generator of the micro-grid according to claim 3, wherein the method comprises the steps of,
in the step 1, according to the mathematical model of the doubly-fed wind turbine, the energy of the generator and the excitation subsystem is obtained through deductionMetering flow W 12 ：
Wherein u is rd 、u rq Respectively the dq-axis component of the rotor voltage, R r Is rotor resistance; i.e sq Representing the q-axis component, e ', of the stator current' d Representation and e' q Representing dq-axis components, X, of respectively transient voltage sources r Reactance for the rotor circuit;
e′ q1 、e′ d1 the expression of (2) is as follows:
5. the method for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator system of the micro-grid, according to claim 4,
in the step 1, the energy flow W of the generator and the excitation subsystem 12 The calculation process of (2) is as follows:
the voltage and flux linkage equations of a doubly fed induction generator are expressed in the rotating dq0 coordinate system as:
wherein u is sd 、u sq Respectively dq axis components of the stator voltage; r is R s 、R r The resistances of the stator and the rotor are respectively; l (L) s 、L r The self-inductance of the stator and the rotor respectively; l (L) m Is the mutual inductance between the stator and the rotor;
using a transient power supply e=e' d +je′ q The three-order simplified model of the doubly-fed induction motor is characterized by comprising the following steps:
in the above, X' =x s +X r ||X m X' is transient reactance;
substituting formula (V) into formula (VI) to obtain:
in the above, de' d /dt、de′ q Dividing dt into two parts including no slip and slip; substituting the formulas (V) and (VII) into the formula (II) to obtain the energy flow W of the generator and the excitation subsystem 12 I.e. formula (IV).
6. The method for analyzing the oscillation characteristics of the output power of the doubly-fed wind turbine generator system of the micro-grid, according to claim 4,
in the step 2, when the wind speed is smaller than the rated wind speed of the unit and larger than the rated wind speed of the unit, the control strategies of the doubly-fed wind turbine are different, and energy functions of wind turbine subsystems in the unit are different, so that when the wind speed is smaller than the rated wind speed of the unit and larger than the rated wind speed of the unit, the influence of wind speed change on subsynchronous oscillation of the unit is analyzed respectively.
7. The method for analyzing the output power oscillation characteristics of the doubly-fed wind turbine generator of the micro-grid according to claim 6, wherein the method comprises the steps of,
in the step 2, when the wind speed is smaller than the rated wind speed of the unit, the influence of the wind speed change on the subsynchronous oscillation of the unit is as follows:
when the doubly-fed wind turbine generator runs normally at rated wind speed, the rotating speed omega of the wind turbine w And generator speed omega g The slip sigma is increased along with the increase of the wind speed, and the slip sigma is reduced along with the increase of the wind speed; in the formula (II), the energy consumed by the shafting of the unit isLetter of (1)Number increases with increasing wind speed; meanwhile, when the wind speed is increased, the slip sigma is reduced, the (1-sigma) is increased, and the consumption energy of a maximum power tracking control system of the wind turbine is increased, so that the damping of a subsystem of the wind turbine is increased along with the increase of the wind speed; in the formula (IV), the energy consumption related to the integral path is the unit slip sigma, sigma 2 And thus W 12 The medium energy consumption is reduced along with the increase of the wind speed, and the damping of the generator and the excitation subsystem is weakened along with the increase of the wind speed;
the energy consumed by the doubly-fed wind turbine generator is determined by the energy consumed by the wind turbine subsystem, the generator and the excitation subsystem together, and the trend along with the change of wind speed is opposite; because the damping coefficient of the shafting of the unit is larger than 1,0 < sigma < 1, and W 12 The seventh term of (2) and the slip square sigma 2 In relation, therefore, the wind speed variation has less influence on the energy consumption of the generator and the excitation subsystem than the wind turbine subsystem; when the wind speed increases, the increase of the energy consumption of the wind turbine subsystem is larger than the decrease of the energy consumption of the generator and the excitation subsystem; the doubly-fed wind turbine generator runs below the rated wind speed, and the energy consumed by the doubly-fed wind turbine generator when the wind speed changes is determined by the wind turbine subsystem and is reduced along with the reduction of the wind speed;
when the electric and control parameters of the doubly-fed wind turbine are set reasonably, and the damping of the doubly-fed wind turbine is strong, the energy consumed by the doubly-fed wind turbine can still keep normal operation even though the energy consumed by the doubly-fed wind turbine is reduced along with the reduction of the wind speed; if the control parameters of the unit converter are improperly set, the unit damping is weakened but still positive damping is achieved, and the unit consumes less energy; when the wind speed is reduced, the energy consumed by the unit is further reduced, and the unit changes from consumed energy to output energy, so that the unit oscillates; if the control parameters of the unit converter are set improperly, the unit is negative damped and subsynchronous oscillation occurs, and then the unit outputs energy; because the energy consumed by the unit is reduced along with the reduction of the wind speed, the output energy of the unit is increased along with the reduction of the wind speed, so that the reduction of the wind speed aggravates the original subsynchronous oscillation of the unit, the amplitude of the output power is increased along with the reduction of the wind speed, and the oscillation frequency drifts along with the change of the wind speed.
8. The method for analyzing the output power oscillation characteristics of the doubly-fed wind turbine generator of the micro-grid according to claim 6, wherein the method comprises the steps of,
in the step 2, when the wind speed is smaller than the rated wind speed of the unit, the influence of the wind speed change on the subsynchronous oscillation of the unit is as follows:
as seen from formula (III), the energy consumed by the wind turbine subsystem is related to the energy consumed by the shafting damping and the energy consumed by the wind turbine impeller; compared with the wind speed which is smaller than the rated wind speed of the unit, the energy consumed by the subsystem of the wind turbine is larger at the moment; when the input wind speed of the wind turbine is rated, the slip ratio of the wind turbine is approaching zero, i.e. sigma is approximately equal to 0, and the energy W of the generator and the excitation subsystem is equal to the energy W of the excitation subsystem 12 The fifth to seventh term in (2) is equal to 0, so that the energy consumed by the generator and the excitation subsystem is smaller at this time compared with the wind speed being less than the rated wind speed of the unit;
when the input wind speed of the wind turbine is greater than the rated wind speed of the unit, the wind turbine enables the unit to operate in a rated state through pitch angle control, and the slip ratio sigma is approximately equal to 0, so that W is obtained 11 And W is 12 And does not change with the input wind speed; the doubly-fed wind turbine generator runs above the rated wind speed, and the energy consumed by the doubly-fed wind turbine generator set when the wind speed changes is determined by the wind turbine subsystem and does not change along with the change of the wind speed; therefore, under various damping states of the doubly-fed wind turbine generator, the wind speed change does not influence the oscillation characteristics of the output power of the generator.
9. The utility model provides a little electric wire netting double-fed wind turbine generator system output oscillation characteristic analysis system which characterized in that includes:
the energy function calculation module is used for calculating an energy function of a wind turbine subsystem, a generator and an excitation subsystem in the doubly-fed wind turbine generator based on a transient energy flow method, a wind speed and a unit control strategy; and the unit oscillation characteristic analysis module is used for analyzing the wind speed and the change mechanism of the energy consumption of each subsystem when the unit control parameters are changed based on the constructed energy functions of the wind turbine subsystem, the generator and the excitation subsystem, so as to obtain the unit oscillation characteristic.
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