CN104135032A - DFIG wind power plant active power scheduling strategy for improving transient stability of wind fire baling system - Google Patents

Abstract

The invention provides a DFIG wind power plant active power scheduling strategy for improving transient stability of a wind fire baling system. The DFIG wind power plant active power scheduling strategy is characterized in that a wind power plant can provide more reactive power for the system in the transient process, transient stability of the system is facilitated, the strategy includes the steps that under fixed force output by a wind power plant, the load rate of a single DFIG is reduced by increasing the number of units of DFIGs input to use of the wind power plant, so that the wind power plant can provide more reactive power for the system in the transient process so as to maintain the bus voltage level. Compared with the prior art, transient stability of a wind fire baling sending end system can be improved without imposing any control measures in the fault process, and the DFIG wind power plant active power scheduling strategy for improving transient stability of the wind fire baling system has the advantages of being scientific and reasonable in scheduling strategy, high in reliability, remarkable in effect and the like.

Description

Improve the meritorious scheduling strategy of DFIG wind energy turbine set of wind fire bundling power system transient stability

Technical field

The present invention relates to technical field of wind power generation, is a kind of meritorious scheduling strategy of DFIG wind energy turbine set that improves wind fire bundling power system transient stability.

Background technology

Large-scale wind power often cannot on-site elimination, needs remote conveying to deliver to load center.Due to the wave characteristic of wind-powered electricity generation, in the time abandoning wind, can cause a large amount of passway for transmitting electricity wastes.The mode that adopts wind fire bundling to send outside can make full use of passway for transmitting electricity, improves the economy of electric power transfer.

It is larger that wind fire bundling system is sent power outside, interconnection trend weight, if impacted by the large disturbances such as short trouble, unstability risk is larger.Therefore, the transient stability of raising wind fire bundling system is very necessary.In existing achievement in research, propose to improve power system transient stability by cutting machine control, can increase the retardation area of synchronous motor after fault clearance, make generator's power and angle recover stable, but life-span and the economic benefit of this method to fired power generating unit all can have a negative impact.Also have some achievements in research about wind energy turbine set internal control; thereby by allow rotor in short-term overcurrent make crow bar protection (Crowbar) be failure to actuate to increase the transient stability of wind-electricity integration; but double-fed type induction generator (double fed induction generator; DFIG) electric current that rotor can bear is limited after all, and this control may still can not make system recover stable sometimes.Therefore, find transient stability that better control method improves wind fire bundling system and become the emphasis of research.

Summary of the invention

Technical problem solved by the invention is, a kind of meritorious scheduling strategy of DFIG wind energy turbine set of scientific and reasonable raising wind fire bundling power system transient stability is provided, can increase the reactive power that DFIG sends in transient process, the electromagnetic power of fired power generating unit after increase failure removal, thus wind fire bundling sending transient stability improved.

The technical scheme that technical solution problem adopts is: a kind of meritorious scheduling strategy of DFIG wind energy turbine set that improves wind fire bundling power system transient stability, it is characterized in that, can make wind energy turbine set provide more reactive power to system in transient process, be conducive to the transient stability of system, it comprise in have:

1) the active power dispatch command P that known wind energy turbine set receives _dFIGthe DFIG number of units n that can put into operation at most with wind energy turbine set;

2) calculate the active power of separate unit DFIG

3) according to existing wind speed v _w, atmospheric density ρ, wind sweeping area A _rthe active-power P that should send with separate unit DFIG _{separate unit DFIG}, calculate wind power efficiency c _p(θ, λ) is the function about propeller pitch angle θ and tip speed ratio λ, by wind power efficiency C _p(θ, λ) and tip speed ratio λ calculate propeller pitch angle θ;

4) provide the control command of each DFIG propeller pitch angle θ.

The meritorious scheduling strategy of DFIG wind energy turbine set of raising wind fire bundling power system transient stability of the present invention compared with prior art, need to not apply any control measure in failure process, just can improve the transient stability of wind fire bundling sending.This scheduling strategy has scientific and reasonable, and reliability is high, the advantage of successful.

Brief description of the drawings

Fig. 1 is wind fire bundling system schematic;

Fig. 2 is DFIG reactive current control link schematic diagram;

Fig. 3 is DFIG reactive current control link schematic diagram;

Fig. 4 is the relatively schematic diagram of reactive current of the DFIG of two examples;

Fig. 5 is the relatively schematic diagram of DFIG set end voltage of two examples;

Fig. 6 is the idle comparison schematic diagram of exerting oneself of the DFIG of two examples;

Fig. 7 is the relatively schematic diagram of bus2 busbar voltage of two examples;

Fig. 8 is the relatively schematic diagram of fired power generating unit active power of two examples;

Fig. 9 is E' and the U of two examples ₂between angle schematic diagram;

Figure 10 is the relatively schematic diagram of fired power generating unit angular speed of two examples;

Figure 11 is the relatively schematic diagram of fired power generating unit merit angle of two examples.

Embodiment

The invention will be further described below.

The meritorious scheduling strategy of DFIG wind energy turbine set that improves wind fire bundling power system transient stability taking simple wind fire bundling system as example explanation is a kind of, as shown in Figure 1, bus1 accesses fired power generating unit, adopts second order classical model in analysis, bus4 access DFIG wind-powered electricity generation unit.T ₀time be engraved in bus2 and bus3 a loop line road there is three-phase shortcircuit, t ₁moment is excised this circuit, fault clearance.

1. wind fire bundling sending Transient Stability Analysis

If Fig. 1 is wind fire bundling system diagram, bus1 accesses fired power generating unit, bus2 access DFIG unit, and bus3 is Infinite bus system.Wherein fired power generating unit adopts second order classical model:

$\frac{\mathrm{d\ω}}{\mathrm{dt}}=\frac{1}{T_J}(P_T-P_e)---\left(1\right)$

$\frac{\mathrm{d\δ}}{\mathrm{dt}}=\mathrm{\Δ\ω}\·{\mathrm{\ω}}_N---\left(2\right)$

Wherein: ω is fired power generating unit rotor velocity, δ is fired power generating unit merit angle, ω _nfor rated angular velocity, the changing value that Δ ω is angular speed, T _jfor fired power generating unit inertia time constant, P _tfor fired power generating unit mechanical output, P _efor fired power generating unit electromagnetic power.

According to law of equal areas, after fault occurs, fired power generating unit electromagnetic power P _elarger, acceleration area is less, and retardation area is larger, is more conducive to power system transient stability.P _ecan be expressed as:

$P_e=\frac{E^{\′}{U}_2}{X_d^{\′}+X_T}\sin {\mathrm{\δ}}_{E^{\′}-U_2}---\left(3\right)$

Wherein: X' _dfor the reactance of fired power generating unit d axle transient state, X _tfor transformer reactance, E' is fired power generating unit transient potential, U ₂for bus2 busbar voltage amplitude, for E' and U ₂angle.

In short time between age at failure and after fault clearance, DFIG load factor pair variable effect little.According to formula (3), U in transient process ₂larger, P _elarger.U ₂can be expressed as:

U ₂＝U ₃+ΔU (4)

Wherein: U ₃for bus3 voltage magnitude, Δ U major decision U ₂with U ₃amplitude poor.Disregard in line resistance situation, Δ U can be expressed as:

$\mathrm{\ΔU}\≈\frac{Q_3{X}_L}{U_2}---\left(5\right)$

Wherein: Q ₃for injecting the reactive power of bus2, X _lfor line reactance.(4) (5) are arranged and can be obtained:

$U_2=\frac{Q_{3}X}{U_2}+U_3---\left(6\right)$

U ₂with the pass of E' be:

Wherein: Q _firefor the reactive power from bus1-bus2 line end.(7) are arranged and can be obtained:

Q ₃=Q _fire+ Q _wind(9)

Wherein: Q _windfor the reactive power from bus4-bus2 line end.(8) (9) substitutions (6) are arranged and can be obtained:

The load factor difference of DFIG can not affect E', U ₃, X _t, X _land X' _d.Known according to formula (10), Q in transient process _windlarger, U ₂higher.

From the reactive power Q of bus4-bus2 line end _windreactive power Q with the output of DFIG unit machine end _{g wind}pass be:

According to formula (11), obviously the reactive power of DFIG unit output is more, and the reactive power of bus4-bus2 line end is more.

Known by above analysis, the reactive power that DFIG injects electrical network in transient process is more, P _ecan be larger, be conducive to the transient stability of this system.

The impact of output on power system transient stability that 2.DFIG is idle

The double-fed fan motor model proposing according to GE electric corporation, meritorious, the reactive power of DFIG can be expressed as:

P＝|V _term|I _p (12)

Q＝|V _term|I _q (13)

Wherein: P is DFIG unit active power, Q is DFIG unit reactive power, V _termfor set end voltage, | V _term| be set end voltage amplitude, I _pfor active current, I _qfor reactive current.

As shown in Figures 2 and 3, obviously reactive current is by changing E for meritorious reactive current control model " _qobtain:

$I_q=\frac{E_q^{\′\′}-\left|V_{\mathrm{term}}\right|}{X^{\′\′}}---\left(14\right)$

Wherein: X " be subtranient reactance, E " _qfor q axle time transient potential.

Formula (13) (14) is arranged and can be obtained:

$Q=\frac{E_q^{\′\′}-\left|V_{\mathrm{term}}\right|-{\left|V_{\mathrm{term}}\right|}^2}{X^{\′\′}}---\left(15\right)$

The equivalent X of DFIG unit " be:

$X^{\′\′}=X_{\mathrm{DFIG}}^{\′\′}\×\frac{U_{\mathrm{DFIG}}^2}{S_{\mathrm{DFIG}}}\×\frac{S_B}{U_B^2}\×k^2---\left(16\right)$

Wherein: X " _dFIGfor the subtranient reactance of DFIG unit, U _dFIGand S _dFIGfor rated voltage and the rated capacity of DFIG unit, U _band S _bfor system reference voltage and reference capacity, k is no-load voltage ratio.

In the identical situation of output of wind electric field and separate unit DFIG parameter, increase the DFIG number of units that puts into operation, can reduce separate unit DFIG load factor.Now S _dFIGcan increase, the equivalent X of DFIG unit " diminishes.Transcient short circuit time E " _qdo not suddenly change, known according to formula (14), " less, set end voltage falls less X, and set end voltage amplitude is higher.

From formula (15), when v _termlarger, Q is larger; When v _termlarger, Q is less." less, Q is for V for X _termand E " _qvariation sensitiveer.In the time of system generation three-phase shortcircuit, V _termfall seriously, due to X, " less, the low DFIG of load factor is at instant of failure V _termhigher, send reactive power larger.

Adopt the DFIG of unity power factor control in failure process, due to the Q of controlling unit _cmdconstant, it is constantly close to steady-state value under the effect of reactive current control link that DFIG sends reactive power.Affect because the running status of each time point is subject to last running status, in fault time-continuing process, the DFIG unit that load factor is lower can provide more reactive powers to system.

At fault clearance moment, V _termhigher than E " _q, there will be reactive current to pour in down a chimney, unit Q is less than 0.Under the effect of reactive current control link, the bottom out of unit reactive power.

After fault clearance, set end voltage gos up, due to X, and " less, the DFIG unit reactive power that load factor is low is gone up higher.

Known by above analysis, output of wind electric field is identical, and the generator number of units putting into operation increases, thereby reduces separate unit DFIG load factor, can make wind energy turbine set provide more reactive power to system in transient process, strengthens the transient stability of system.

3. meritorious scheduling strategy

Based on above theory analysis, meritorious scheduling strategy is proposed as follows:

1) the active power dispatch command P that known wind energy turbine set receives _dFIGthe DFIG number of units n that can put into operation at most with wind energy turbine set;

2) calculate the active power of separate unit DFIG

4) according to existing wind speed v _w, atmospheric density ρ, wind sweeping area A _rthe active-power P that should send with separate unit DFIG _{separate unit DFIG}, calculate wind power efficiency c _p(θ, λ) is the function about propeller pitch angle θ and tip speed ratio λ, by wind power efficiency C _p(θ, λ) and tip speed ratio λ calculate propeller pitch angle θ;

4) provide the control command of each DFIG propeller pitch angle θ.

Concrete application example: wind fire bundling system shown in Figure 1, three-phase shortcircuit appears in the loop line road at bus2 and bus3 when 1s, excises this circuit, fault clearance when 1.22s.Use Based on Power System Analysis Software Package (PSASP) to carry out emulation to this fault, generator adopts 2 rank models.The fired power generating unit 100MW that exerts oneself, wind-powered electricity generation unit output 30MW.In the time that wind energy turbine set adopts 30 fully loaded 1MW set grid-connections, system unstability.And the control strategy proposing according to the present invention increases the DFIG number of units that wind energy turbine set puts into operation, when 100 DFIG of wind energy turbine set are incorporated into the power networks, system is final recovers stable.

Can find out from Fig. 4, Fig. 5 and Fig. 6, adopt in the situation that 100 DFIG are incorporated into the power networks, the reactive current of wind energy turbine set in transient process is larger, and set end voltage is higher, provides more reactive power to system.Known according to formula (10), because the wind energy turbine set of 100 DFIG provides more reactive power to system, therefore bus2 busbar voltage is higher, as Fig. 7.Known according to formula (3), bus2 busbar voltage is higher, and fired power generating unit electromagnetic power is higher, as Fig. 8.And in formula (3) as shown in Figure 9, two examples before system unstability almost identical.Known according to formula (1) (2), fired power generating unit electromagnetic power is higher, and power system transient stability is better, and the merit angle of fired power generating unit and angular speed are as shown in Figure 10 and Figure 11.

More DFIG of visible employing put into operation, thereby reduce separate unit DFIG load factor, can increase wind fire bundling power system transient stability.

Claims (1)

1. the meritorious scheduling strategy of DFIG wind energy turbine set that improves wind fire bundling power system transient stability, is characterized in that, can make wind energy turbine set provide more reactive power to system in transient process, is conducive to the transient stability of system, it comprise in have:

1) the active power dispatch command P that known wind energy turbine set receives _dFIGthe DFIG number of units n that can put into operation at most with wind energy turbine set;

2) calculate the active power of separate unit DFIG

3) according to existing wind speed v _w, atmospheric density ρ, wind sweeping area A _rthe active-power P that should send with separate unit DFIG _{separate unit DFIG}, calculate wind power efficiency c _p(θ, λ) is the function about propeller pitch angle θ and tip speed ratio λ, by wind power efficiency C _p(θ, λ) and tip speed ratio λ calculate propeller pitch angle θ;

4) provide the control command of each DFIG propeller pitch angle θ.