CN112952896A - Power angle stability enhancement control method for voltage source type double-fed fan - Google Patents

Power angle stability enhancement control method for voltage source type double-fed fan Download PDF

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CN112952896A
CN112952896A CN202011159340.0A CN202011159340A CN112952896A CN 112952896 A CN112952896 A CN 112952896A CN 202011159340 A CN202011159340 A CN 202011159340A CN 112952896 A CN112952896 A CN 112952896A
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power angle
dfig
current
virtual power
virtual
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洪敏�
辛焕海
赖全怡
应有
黄林彬
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Zhejiang Windey Co Ltd
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Zhejiang Windey Co Ltd
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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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/007—Control circuits for doubly fed generators
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2101/00—Special adaptation of control arrangements for generators
    • H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines

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  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention provides a power angle stability enhancement control method for a voltage source type double-fed fan, which comprises the following steps of: defining a virtual power angle delta as an included angle between a d axis and the voltage of a power grid, and analyzing the transient stability of the voltage source type DFIG power angle under the working conditions of current unsaturation and current amplitude limiting by using the virtual power angle delta; performing power angle stability enhancement control to control the voltage V of the stator of the voltage source type doubly-fed fanqThe component is used as a nonlinear auxiliary component of the P-f droop ring to construct a new virtual power angle curve. The invention can solve the problem that under the condition of large interference, the voltage source type double-fed fan is caused by self characteristics andtransient power angle instability caused by the current limiting link of the converter is solved, the original stable operation state can be recovered after the fault is cleared, and the static power angle stability margin of the converter is effectively improved.

Description

Power angle stability enhancement control method for voltage source type double-fed fan
Technical Field
The invention relates to the technical field of voltage source type double-fed fans, in particular to a power angle stability enhancement control method for a voltage source type double-fed fan
Background
With the continuous improvement of the wind power grid-connected capacity, the problems that the rotational inertia of the existing power system is lost, the frequency stability of the system is reduced and the like are further serious due to the fact that a large number of double-fed wind generating sets are connected through the power electronic device. The voltage source type droop control technology can enable a Doubly Fed Induction Generator (DFIG) to display voltage source characteristics by simulating the operation characteristics of a traditional synchronous Generator, improve grid-connected equivalent inertia of the Doubly fed Induction Generator and wind energy permeability of a power grid, and provide voltage and frequency support for the power grid. Research shows that under the condition of large interference, the voltage source type double-fed wind turbine has the similar power angle characteristic with the traditional synchronous generator. And because of the nonlinearity of a sine function in the output power, the voltage source type double-fed fan has a potential synchronous stability problem as a synchronous generator. In addition, due to the current limiting control in the converter, the voltage source type double-fed fan can be degenerated into a current source due to the amplitude limiting of current under the condition of large interference, and the instability process of the voltage source type double-fed fan is more complicated due to the characteristic. Therefore, the problem of power angle stability of the voltage source type double-fed fan is worthy of further research. In the past documents, two methods are mainly used for solving the problem of transient power angle instability of a voltage source type double-fed fan under large disturbance, one method is to increase virtual impedance when current output of a converter reaches a saturation value, and the scheme can enable a system to recover to an original stable operation state after fault clearing, but can not effectively increase power angle stability; the other is a control method for switching the converter when large disturbance is detected, and the scheme increases the power angle stability but cannot enable the system to recover to an initial stable operation state. These two methods add many extra parameters and require on-line fault detection and control switching, which is complex to implement. Under big interference, the transient state power angle unstability similar with traditional synchronous generator can appear in voltage source type double-fed fan, can degenerate into a current source because of the current amplitude limit of converter moreover, further worsens synchronous stability, leads to virtual power angle transient state unstability to be difficult to restore to original state after the trouble excision.
Disclosure of Invention
The invention solves the problem of transient power angle instability of a voltage source type double-fed fan caused by self characteristics and a current limiting link of a converter, provides a power angle stability enhancement control method of the voltage source type double-fed fan, can solve the problem of transient power angle instability of the voltage source type double-fed fan caused by self characteristics and the current limiting link of the converter under large interference, can recover the original stable operation state after a fault is eliminated, and effectively improves the static power angle stability margin of the voltage source type double-fed fan.
In order to realize the purpose, the following technical scheme is provided:
a power angle stability enhancement control method for a voltage source type double-fed fan comprises the following steps:
s1, defining a virtual power angle delta as an included angle between the d axis and the voltage of the power grid, and analyzing the transient stability of the voltage source type DFIG power angle under the current unsaturated and current amplitude limiting working conditions by using the virtual power angle delta;
s2, performing power angle stability enhancement control, and controlling the voltage V of the stator of the voltage source type doubly-fed fanqThe component is used as a nonlinear auxiliary component of the P-f droop ring to construct a new virtual power angle curve.
Preferably, the step S1 specifically includes:
s101, virtual power angle in steady state
Figure RE-GDA0003011192230000021
Wherein
Figure RE-GDA0003011192230000022
Is the voltage of the power grid,
Figure RE-GDA0003011192230000023
for the DFIG stator voltage value, the relation between the virtual power angle and the P-f droop ring is deduced as follows:
Figure RE-GDA0003011192230000024
where δ is the derivative of the virtual power angle, θ is the d-axis phase determined by P-f droop control, θgFor mains voltage
Figure RE-GDA0003011192230000025
Phase of (P)0And PsRespectively setting values and output values of active power of a DFIG stator;
s102, under the current unsaturated working condition, the stator power of the voltage source type doubly-fed fan is as follows:
Figure RE-GDA0003011192230000026
wherein X∑In order to obtain the equivalent impedance of the line,
Figure RE-GDA0003011192230000027
the output current of the DFIG increases along with the increase of the virtual power angle, and when the output current reaches ImaxAnd then, the virtual power angle also reaches the maximum value under the current unsaturated working condition:
δmax＝arcsin(Pm/Pum)
s103, under the current amplitude limiting working condition, the voltage source type double-fed fan outputs power:
Ps＝Re(UgImax)＝ImaxUcosδ＝ImaxUsin(δ+90°)＝Psmsin(δ+90°)
wherein P issm＝ImaxU, under the current unsaturated working condition, the stator current of the DFIG increases along with the increase of the virtual power angle, and when the output current reaches ImaxAnd when the current is not saturated, the virtual power angle reaches the maximum value under the current unsaturated working condition:
δmax＝arcsin(Pm/Pum)
wherein P ismThe maximum value of the output power of the DFIG in the state is as follows:
Figure RE-GDA0003011192230000031
when the virtual power angle reaches deltamaxWhen the DFIG enters the current amplitude limiting working condition, the DFIG is analyzed according to the power angle stability, and when P is obtainedm＞P0And in addition, the system can keep the power angle stable.
Preferably, the step S1 further includes analyzing the transient stability of the voltage source doubly-fed wind turbine under the large disturbance of the grid voltage drop, and specifically includes:
s104, when the grid voltage drop value U' is less than P0/Imax：
At this time Psm＜P0The virtual power angle will increase until it is unstable; considering fault clearance, there is a critical cut-off angle δ'CC＝arccos(P0/Psm) When the virtual power angle is less than delta'CCWhen the fault is cleared, the DFIG can return to the initial stable state, and when the virtual power angle is larger than delta'CCWhen the fault is cleared, the DFIG will lose stability of the power angle;
s105, the grid voltage drop value U' is more than P0/Imax：
At this time Psm＞P0The virtual power angle is reduced to a power angle stable point c' all the time, the power angle stable point is on the left half plane of the power angle curve coordinate system, fault clearing is considered, the virtual power angle is continuously reduced to a new power angle stable point c, but due to the fact that the unsaturated curve is on the right half plane, the DFIG cannot be recovered to the initial stable point, and can only operate at a new stable point under the saturated current working condition all the time.
Preferably, the new virtual power angle curve of step S2 is:
Figure RE-GDA0003011192230000032
wherein KASIs the power angle stability enhancement factor, VqIs the stator voltage
Figure RE-GDA0003011192230000033
Q-cycle of (2), when KASWhen the power angle stability enhancement control is 0, the power angle stability enhancement control is converted into the classic P-f droop control.
Preferably, the step S2 further includes calculating power of the virtual power angle curve, and determining the static power angle stability margin of the DFIG, including:
δ＝ω*-ω0＝KP(P0-Ps)+KASVq＝KP(P0-S)
Figure RE-GDA0003011192230000034
and obtaining the power of a virtual power angle curve through a stator voltage equation:
Figure RE-GDA0003011192230000035
wherein
Figure RE-GDA0003011192230000041
Figure RE-GDA0003011192230000042
With KASThe maximum value of the virtual power angle curve power is increased, the DFIG keeps the static power angle stable when disturbance occurs, and the judgment basis is Smax＞P0：
Figure RE-GDA0003011192230000043
Preferably, the step S2 further includes calculating a grid voltage drop range within which the DFIG can maintain the static power angle stable by adding the power angle stability enhancement control:
Figure RE-GDA0003011192230000044
preferably, the step S2 further includes a step of proving that the transient power angle stability of the DFIG can be significantly improved under the power angle stability enhancement control, and specifically includes that the transient virtual power angle characteristic under the large interference is also changed, and is stabilized at the point a under the current unsaturated condition, and when the grid voltage drops, the DFIG enters the current limiting condition and is moved from the point a to the point a', because of P, the DFIG enters the current limiting condition0S 'is increased, delta is moved to a new stable point c', after the fault is cleared, U is 1.0, the virtual power angle curve is changed, the virtual power angle working point of the DFIG is changed from c 'to c', and P is provided again at the moment0If the virtual power angle delta is reduced to reach an initial stable point a, the DFIG is switched to operate under the current unsaturated working condition, and after the power angle stability enhancement control is added, the static power angle stability margin of the DFIG is greatly improved; when suffering from large interference of voltage drop, the transient power angle can be kept stable, a new stable operation point is reached, and after the fault is cleared, the initial stable operation state can be recovered.
The invention has the beneficial effects that:
1. under the condition of large interference, the problem of transient power angle instability of the voltage source type double-fed fan can be restrained, and after the fault is eliminated, the original stable operation state is recovered;
2. the static power angle stability margin of the voltage source type double-fed fan can be effectively improved;
3. the method is simple and feasible, does not need fault detection and control switching, only comprises one adjustable parameter, and does not generate a gain effect when the voltage source type double-fed fan stably operates.
Drawings
FIG. 1 is a control block diagram of a voltage source type doubly-fed wind turbine of an embodiment;
FIG. 2 is a diagram of DFIG phasor relationships based on virtual synchronous control according to an embodiment;
FIG. 3 is a virtual power angle transient response at voltage droop of an embodiment;
FIG. 4 is a control block diagram of a power angle stability enhancement control method of an embodiment;
FIG. 5 is a virtual power angle curve for different KAS values under power angle stability enhancement control of an embodiment;
fig. 6 is a transient virtual power angle curve under the power angle stability enhancement control of the embodiment.
Detailed Description
Example (b):
the embodiment provides a power angle stability enhancement control method for a voltage source type doubly-fed wind turbine, which takes the case that a single DFIG is merged into an infinite system as an example, and by taking the concept and method (power angle, power angle characteristic curve and the like) of analyzing the transient stability of a synchronous generator in an electric power system as reference, describes the motion change of the voltage source type doubly-fed wind turbine by defining the virtual power angle of the voltage source type doubly-fed wind turbine, and analyzes the virtual power angle transient instability mechanism of the voltage source type doubly-fed wind turbine under the current amplitude limiting action according to the motion change.
The voltage source type doubly-fed wind turbine usually adopts a three-loop control mode based on a power control loop-voltage control loop-current control loop, and a typical control block diagram of the voltage source type doubly-fed wind turbine is shown in fig. 1. Generally, the 3 control links belong to different time scales respectively, and the dynamic of the current control loop is faster than that of the voltage control loop, and the dynamic of the voltage control loop is faster than that of the power control loop. Considering that the transient stability problem of the converter is mainly dominated by a power control loop (droop control), in order to simplify the transient stability analysis process, the dynamics of the voltage control loop and the current control loop can be generally ignored, that is, the voltage source type doubly-fed wind turbine is considered to be a controlled voltage source, the amplitude reference of the voltage is derived from a Q-V (reactive power-voltage) droop loop, and the frequency reference is derived from a P-f (active power-frequency) droop loop, as shown in formulas (1) and (2).
Figure RE-GDA0003011192230000051
Vref-V0＝KQ(Q0-Qs) (2)
Wherein:
Figure RE-GDA0003011192230000052
and ω0Respectively, the frequency and the reference value of the stator voltage of the doubly-fed fan, VrefAnd V0Respectively a DFIG stator voltage reference value and a reference value, P0And PsRespectively a given value and an output value of active power of a DFIG stator, Q0And QsRespectively a given value and an output value of the reactive power of the DFIG stator, KPAnd KQP-f and Q-V droop control coefficients, respectively.
Because overcurrent can lead to the converter to damage, consequently often restrict the output current of converter in control, through Clark and Park transform after, often adopt dynamic amplitude limiting link:
Figure RE-GDA0003011192230000061
wherein
Figure RE-GDA0003011192230000062
And
Figure RE-GDA0003011192230000063
for the reference output value of the rotor current before the voltage loop amplitude limiting, IrmaxThe maximum allowable current value of the converter. When the amplitude of the output current does not reach the maximum allowable current value, the operating state of the converter is a current unsaturated state, when the amplitude of the output current reaches the maximum allowable current value, the operating state of the converter is a current amplitude limiting state, and at the moment, the stator current can be known from the current relation between the stator and the rotor of the double-fed fan
Figure RE-GDA0003011192230000064
Also reaches the maximum value in this state
Figure RE-GDA0003011192230000065
In the current unsaturated state, the voltage source type doubly-fed wind turbine can be regarded as a controlled voltage source, the phase and amplitude of the voltage source are determined by the P-f and Q-V droop rings, the d-axis phase is set to be determined by the P-f droop ring, and then the d-axis position and DF are determined in the steady stateIG stator voltage phasor
Figure RE-GDA0003011192230000066
Coincidence, then has VqNote that due to the presence of voltage outer loop dynamics, the d-axis phase and during transients
Figure RE-GDA0003011192230000067
And do not coincide. When the current amplitude limiting state is realized, the voltage source type double-fed fan can be regarded as a controlled current source, and the phase and the amplitude of the current source are determined by the P-f droop ring and the current amplitude limiting link. From the equation (3), the stator current phasor
Figure RE-GDA0003011192230000068
Locked on the d-axis.
Regarding the power angle stability problem of the voltage source type doubly-fed wind turbine, the problem can be similar to that of a synchronous machine, namely, whether the virtual power angle can be recovered to an initial stable state or a new stable state after suffering from large disturbance such as voltage drop.
S101, a virtual power angle delta is defined as an included angle between a d axis (determined by a P-f droop ring) and the voltage of a power grid, and the power grid is in a steady state
Figure RE-GDA0003011192230000069
The equivalent model is shown in FIG. 2, wherein
Figure RE-GDA00030111922300000610
Is the voltage of the power grid,
Figure RE-GDA00030111922300000611
and deducing the relation between the virtual power angle and the P-f droop ring for the DFIG stator voltage value as shown in the formula (4). Obviously, the DFIG can be kept in a synchronous operation state only if the virtual power angle is maintained to be stable, so that the problem of the transient power angle stability of the voltage source type double-fed fan can be analyzed by researching the transient stability of the virtual power angle.
Figure RE-GDA00030111922300000612
Where δ is the derivative of the virtual power angle, θ is the d-axis phase determined by P-f droop control, θgFor mains voltage
Figure RE-GDA00030111922300000613
Phase of (P)0And PsRespectively is a given value and an output value of the active power of the DFIG stator.
S102, under the current unsaturated working condition, the stator power of the voltage source type doubly-fed wind turbine can be represented by an equation (5):
Figure RE-GDA00030111922300000614
wherein X∑In order to obtain the equivalent impedance of the line,
Figure RE-GDA0003011192230000071
s103, under the current amplitude limiting working condition, the stator power of the voltage source type doubly-fed wind turbine can be represented by the formula (6):
Ps＝Re(UgImax)＝ImaxUcosδ＝ImaxUsin(δ+90°)＝Psmsin(δ+90°)
(6)
wherein P issm＝ImaxAnd U is adopted. Under the current unsaturated working condition, the stator current of the DFIG is increased along with the increase of the virtual power angle, and when the output current reaches ImaxAnd then, the virtual power angle also reaches the maximum value under the current unsaturated working condition:
δmax＝arcsin(Pm/Pum) (7)
wherein P ismThe maximum value of the output power of the DFIG in the state is as follows:
Figure RE-GDA0003011192230000072
when virtual workAngle up to deltamaxWhen the DFIG enters the current amplitude limiting working condition, according to the stable analysis of the power angle, only when P is known easilym＞P0And in addition, the system can keep the power angle stable.
The scheme mainly researches the transient power angle stability of the voltage source type double-fed fan under the large disturbance of the voltage drop of the power grid. When the voltage of the power grid drops, the current output of the DFIG reaches the maximum value, the DFIG operates in a current saturation working condition, and the maximum value P of the virtual power angle curve is under the two working conditionsumAnd PsmDue to the reduction of the voltage drop of the power grid, the power angle curve analysis of the synchronous generator can be referred, and the discussion is divided into two cases:
s104, the grid voltage drop value U' is less than P0/Imax
As shown in FIG. 3(a), the grid voltage U' falls to P0/ImaxWhen the following is Psm＜P0The virtual power angle will increase until it is unstable; considering fault clearance, there is a critical cut-off angle δ'CC＝arccos(P0/Psm) When the virtual power angle is less than delta'CCWhen the fault is cleared, the DFIG can return to the initial stable state, and when the virtual power angle is larger than delta'CCWhen the fault is cleared, the DFIG will lose the power angle.
S105, the grid voltage drop value U' is more than P0/Imax
As shown in fig. 3(b), the grid voltage drops U' to P0/ImaxWhen above, there is Psm＞P0When the current amplitude limiting working condition is entered, the current amplitude limiting working condition is started because of Psm＞P0The virtual power angle is always reduced to a power angle stabilizing point c', which is on the left half plane of the power angle curve coordinate system, and the virtual power angle is continuously reduced to a new power angle stabilizing point c in consideration of fault clearance.
Aiming at the problem of power angle instability of DFIG under the current amplitude limiting working condition, the invention carries out power angle stabilityThe strategy core of the fixed enhancement control is to apply the V of the stator voltage of the voltage source type doubly-fed wind turbineqThe component is used as a nonlinear auxiliary component of a P-f droop ring, and a new virtual power angle curve is constructed:
Figure RE-GDA0003011192230000081
wherein KASIs the power angle stability enhancement factor, VqIs the stator voltage
Figure RE-GDA0003011192230000082
Q-cycle of (2), when KASWhen the power angle stability enhancement control is 0, the power angle stability enhancement control is converted into the classic P-f droop control.
The power angle stability enhancement control block diagram is shown in fig. 4, and only one parameter K needing to be adjusted is providedASAt steady state, VqPower angle stability enhancement module K equal to 0ASVqDoes not play a role, and does not influence the DFIG under the normal operation working condition.
1) Virtual power angle curve with power angle stability enhancement control
The virtual power angle curve containing power angle stability enhancement control under the condition of grid voltage drop is analyzed as follows:
δ＝ω*-ω0＝KP(P0-Ps)+KASVq＝KP(P0-S) (10)
Figure RE-GDA0003011192230000083
under the current amplitude limiting working condition, the virtual power angle characteristic curve changes, the line resistance is ignored, and the DFIG stator voltage equation is as follows:
Figure RE-GDA0003011192230000084
wherein VdqAnd Udq、IdqDq axis components of V, U and I, respectively, I being the DFIG stator current vector, X∑Is the line equivalent impedance.
From fig. 2 it can be derived that:
Figure RE-GDA0003011192230000085
substituting (13) into (12) yields:
Vq＝-Usinδ+X∑Id (14)
substituting (6) and (14) into (11) yields:
Figure RE-GDA0003011192230000086
wherein
Figure RE-GDA0003011192230000091
According to (16), the difference K can be plottedASThe virtual work angle curve under the value is shown in fig. 5. With KASThe maximum value of the virtual power angle curve is increased, and the analysis shows that the maximum value S of the power of the virtual power angle curve under the current amplitude limiting working condition is improvedmaxAnd the power angle stability margin is increased. But when S ismaxLess than P0When disturbance occurs, power angle instability still occurs. Therefore, the DFIG keeps the static power angle stable when the disturbance occurs, and the judgment basis is Smax＞P0：
Figure RE-GDA0003011192230000092
Binding to Smax＞P0And (17), the grid voltage drop range of the DFIG capable of keeping the static power angle stable can be obtained:
Figure RE-GDA0003011192230000093
2) transient stability of DFIG under power angle stability enhancement control
The power angle stability enhancement control changes a virtual power angle curve under the current limiting working condition, the transient virtual power angle characteristic under the large interference is changed, as shown in fig. 6, under the current unsaturated working condition, the operation state of the DFIG is determined by (4) and (5), the DFIG is stabilized at a point a, when the voltage of a power grid drops, the DFIG enters the current limiting working condition and moves from the point a to the point a', and due to the fact that P is greater than P, the DFIG enters the current limiting working condition and moves from the point a to the point a0S 'is increased, delta is moved to a new stable point c', after the fault is cleared, U is 1.0, the virtual power angle curve is changed, the virtual power angle working point of the DFIG is changed from c 'to c', and P is provided again at the moment0< S', therefore, delta decreases until an initial stable point a is reached and the DFIG switches to operation in a current unsaturated regime.
3) According to the analysis, after the power angle stability enhancement control is added, the static power angle stability margin of the DFIG is greatly improved; when suffering from large interference of voltage drop, the transient power angle can be kept stable, a new stable operation point is reached, and after the fault is cleared, the initial stable operation state can be recovered.
The invention has the beneficial effects that:
1. under the condition of large interference, the problem of transient power angle instability of the voltage source type double-fed fan can be restrained, and after the fault is eliminated, the original stable operation state is recovered;
2. the static power angle stability margin of the voltage source type double-fed fan can be effectively improved;
3. the method is simple and feasible, does not need fault detection and control switching, only comprises one adjustable parameter, and does not generate a gain effect when the voltage source type double-fed fan stably operates.

Claims (7)

1. A power angle stability enhancement control method for a voltage source type double-fed fan is characterized by comprising the following steps:
s1, defining a virtual power angle delta as an included angle between the d axis and the voltage of the power grid, and analyzing the transient stability of the voltage source type DFIG power angle under the current unsaturated and current amplitude limiting working conditions by using the virtual power angle delta;
s2, performing power angle stability enhancement control, and controlling the voltage V of the stator of the voltage source type doubly-fed fanqThe component is used as a nonlinear auxiliary component of the P-f droop ring to construct a new virtual power angle curve.
2. The method according to claim 1, wherein the step S1 specifically includes:
s101, virtual power angle in steady state
Figure RE-FDA0003011192220000011
Wherein
Figure RE-FDA0003011192220000012
Is the voltage of the power grid,
Figure RE-FDA0003011192220000013
for the DFIG stator voltage value, the relation between the virtual power angle and the P-f droop ring is deduced as follows:
Figure RE-FDA0003011192220000014
where δ is the derivative of the virtual power angle, θ is the d-axis phase determined by P-f droop control, θgFor mains voltage
Figure RE-FDA0003011192220000015
Phase of (P)0And PsRespectively setting values and output values of active power of a DFIG stator;
s102, under the current unsaturated working condition, the stator power of the voltage source type doubly-fed fan is as follows:
Figure RE-FDA0003011192220000016
wherein X∑In order to obtain the equivalent impedance of the line,
Figure RE-FDA0003011192220000017
the output current of the DFIG increases along with the increase of the virtual power angle, and when the output current reaches ImaxAnd then, the virtual power angle also reaches the maximum value under the current unsaturated working condition:
δmax＝arcsin(Pm/Pum)
s103, under the current amplitude limiting working condition, the voltage source type double-fed fan outputs power:
Ps＝Re(UgImax)＝ImaxUcosδ＝ImaxUsin(δ+90°)＝Psmsin(δ+90°)
wherein P issm＝ImaxU, under the current unsaturated working condition, the stator current of the DFIG increases along with the increase of the virtual power angle, and when the output current reaches ImaxAnd when the current is not saturated, the virtual power angle reaches the maximum value under the current unsaturated working condition:
δmax＝arcsin(Pm/Pum)
wherein P ismThe maximum value of the output power of the DFIG in the state is as follows:
Figure RE-FDA0003011192220000021
when the virtual power angle reaches deltamaxWhen the DFIG enters the current amplitude limiting working condition, the DFIG is analyzed according to the power angle stability, and when P is obtainedm＞P0And in addition, the system can keep the power angle stable.
3. The method according to claim 2, wherein the step S1 further includes analyzing the transient stability of the voltage source doubly-fed wind turbine under the large disturbance of the grid voltage drop, and specifically includes:
s104, when the grid voltage drop value U' is less than P0/Imax：
At this time Psm＜P0The virtual power angle will increase until it is unstable; considering fault clearance, there is a critical cut-off angle δ'CC＝arccos(P0/Psm) When the virtual power angle is less than delta'CCWhen the fault is cleared, the DFIG can return to the initial stable state, and when the virtual power angle is larger than deltaC′CWhen the fault is cleared, the DFIG will lose stability of the power angle;
s105, the grid voltage drop value U' is more than P0/Imax：
At this time Psm＞P0The virtual power angle is reduced to a power angle stable point c' all the time, the power angle stable point is on the left half plane of the power angle curve coordinate system, fault clearing is considered, the virtual power angle is continuously reduced to a new power angle stable point c, but due to the fact that the unsaturated curve is on the right half plane, the DFIG cannot be recovered to the initial stable point, and can only operate at a new stable point under the saturated current working condition all the time.
4. The method according to claim 2 or 3, wherein the new virtual power angle curve of step S2 is:
Figure RE-FDA0003011192220000022
wherein KASIs the power angle stability enhancement factor, VqIs the stator voltage
Figure RE-FDA0003011192220000023
Q-cycle of (2), when KASWhen the power angle stability enhancement control is 0, the power angle stability enhancement control is converted into the classic P-f droop control.
5. The method according to claim 4, wherein the step S2 further includes calculating power of a virtual power angle curve, and determining a static power angle stability margin of the DFIG, and specifically includes:
δ＝ω*-ω0＝KP(P0-Ps)+KASVq＝KP(P0-S)
Figure RE-FDA0003011192220000024
and obtaining the power of a virtual power angle curve through a stator voltage equation:
Figure RE-FDA0003011192220000031
wherein
Figure RE-FDA0003011192220000032
Figure RE-FDA0003011192220000033
With KASThe maximum value of the virtual power angle curve power is increased, the DFIG keeps the static power angle stable when disturbance occurs, and the judgment basis is Smax＞P0：
Figure RE-FDA0003011192220000034
6. The method according to claim 4, wherein the step S2 further includes calculating a grid voltage drop range within which the DFIG can maintain the static power angle stable by adding the power angle stability enhancement control:
Figure RE-FDA0003011192220000035
7. the method according to claim 4, wherein the step S2 further comprises a step of proving that the transient power angle stability of the DFIG can be significantly improved under the power angle stability enhancement control, and specifically comprises that the transient virtual power angle characteristic under the large interference is changed, the DFIG is stabilized at a point a under the current unsaturated condition, and when the grid voltage drops, the DFIG enters the current limiting condition and moves from the point a to a' due to the fact that P is a point0S 'is increased, delta is moved to a new stable point c', after the fault is cleared, U is 1.0, the virtual power angle curve is changed, the virtual power angle working point of the DFIG is changed from c 'to c', and P is provided again at the moment0If the virtual power angle delta is reduced to reach an initial stable point a, the DFIG is switched to operate under the current unsaturated working condition, and after the power angle stability enhancement control is added, the static power angle stability margin of the DFIG is greatly improved; when suffering from large interference of voltage drop, the transient power angle can be kept stable, a new stable operation point is reached, and after the fault is cleared, the initial stable operation state can be recovered.
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