CN104158225A - Wind energy caching low voltage ride through and reactive supporting control method for double-feed draught fan - Google Patents

Abstract

The invention discloses a wind energy caching low voltage ride through and reactive supporting control method for a double-feed draught fan and belongs to the technical field of automatic control over wind driven generators. The purpose of reducing the currents of a rotor is achieved by switching electromagnetic torque reference values in a rotor side (RSC) control circuit under grid faults and temporarily storing surplus wind energy captured under the faults into rotor inertia energy. After the voltage recovers, a traditional circuit is switched back by an RSC, after the switch, overcurrent of the voltage recovery segment is avoided by temporarily limiting the electromagnetic torque of the RSC, and energy balance recovers safely. After a cascading feedback type reactive controller is applied, a fan can also provide reactive supporting safely for a grid in the whole low voltage ride through process. Compared with the prior art, the method is high in control strategy speed, new hardware is not introduced in, fault current in the fan can be effectively reduced, grid leaving time is prolonged, and nearby voltage can be obviously stabilized.

Description

A kind of double-fed blower fan low voltage crossing of buffer memory wind energy and reactive power support control method

Technical field

The invention belongs to wind-driven generator automatic control technology field, more precisely, the present invention relates to a kind of double-fed blower fan low voltage crossing and reactive power support control method of buffer memory wind energy.

Background technology

Double-fed wind power generator (double-fed blower fan) is used widely because of its high efficiency, variable-speed operation, meritorious idle independent control.Under nominal situation, in double-fed blower fan control system, extensive use be take max power point tracking and is caught control (MPPT) method as controlling the optimal wind energy of target, and its schematic diagram as shown in Figure 1.

MPPT method is applied five rank dynamic models, and the state equation of employing formula (1) is described generator model:

$\left\{\begin{array}{c}{u}_{\mathrm{ds}}=R_s{i}_{\mathrm{ds}}-{\mathrm{\ω}}_s{\mathrm{\ψ}}_{\mathrm{qs}}+\frac{1}{{\mathrm{\ω}}_b}\frac{{\mathrm{d\ψ}}_{\mathrm{ds}}}{\mathrm{dt}}\\ u_{\mathrm{qs}}{R}_s{i}_{\mathrm{qs}}+{\mathrm{\ω}}_s{\mathrm{\ψ}}_{\mathrm{ds}}+\frac{1}{{\mathrm{\ω}}_b}\frac{{\mathrm{d\ψ}}_{\mathrm{qs}}}{\mathrm{dt}}\\ u_{\mathrm{dr}}=R_r{i}_{\mathrm{dr}}-{\mathrm{s\ω}}_s{\mathrm{\ψ}}_{\mathrm{qr}}+\frac{1}{{\mathrm{\ω}}_b}\frac{{\mathrm{d\ψ}}_{\mathrm{dr}}}{\mathrm{dt}}\\ u_{\mathrm{qr}}=R_r{i}_{\mathrm{qr}}+{\mathrm{s\ω}}_s{\mathrm{\ψ}}_{\mathrm{dr}}+\frac{1}{{\mathrm{\ω}}_b}\frac{{\mathrm{d\ψ}}_{\mathrm{qr}}}{\mathrm{dt}}\end{array}\right.---\left(1\right)$

Wherein, u _s=u _ds+ ju _qswith u _r=u _dr+ ju _qrrepresent respectively stator and rotor voltage vector, i _s=i _ds+ ji _qswith i _r=i _dr+ ji _qrrepresent respectively stator and rotor current vector, ψ _s=ψ _ds+ j ψ _qswith ψ _r=ψ _dr+ j ψ _qrrepresent respectively stator and rotor flux.ω _b, ω _sbe respectively reference angle frequency and stator angular frequency, s is slip.System model, except the unit of time t is second, all adopts perunit value.

The electromagnetic torque of generator is produced by armature reaction, has determined given time has how much mechanical energy (deriving from wind energy) to be converted to electric energy, and formula (2) has been described electromagnetic torque T _eand the relation between stator, rotor current, L _mrepresent the mutual inductance of rotor coil.

T _e＝L _m(i _qsi _dr-i _dsi _qr) (2)

Adopt the wind energy conversion system drive system differential equation group of two matter block models descriptions suc as formula shown in (3).

$\left\{\begin{array}{c}\frac{{\mathrm{d\ω}}_r}{\mathrm{dt}}=\frac{1}{{2H}_g}(T_{\mathrm{sh}}-T_e-{\mathrm{B\ω}}_r)\\ \frac{{\mathrm{d\θ}}_t}{\mathrm{dt}}={\mathrm{\ω}}_b({\mathrm{\ω}}_t-{\mathrm{\ω}}_r)\\ \frac{{\mathrm{d\ω}}_t}{\mathrm{dt}}\frac{1}{{2H}_t}(T_t-T_{\mathrm{sh}})\\ T_{\mathrm{sh}}=K_{\mathrm{sh}}{\mathrm{\θ}}_t+D_{\mathrm{sh}}{\mathrm{\ω}}_b({\mathrm{\ω}}_t-{\mathrm{\ω}}_r)\end{array}\right.---\left(3\right)$

Wherein, ω _bfor reference angle frequency, ω _rrepresent generator amature rotating speed, ω _tthe rotating speed that represents wind energy conversion system, θ _tthe torsion angle that represents power transmission shaft, H _gand H _tbe respectively the inertia constant (unit is second) of generator and wind energy conversion system, B, K _shand D _shbe respectively generator coefficient of friction, power transmission shaft stiffness (stiffness) and damping factor (damping coefficient).T _t, T _sh, T _erepresent respectively wind energy conversion system machine torque, power transmission shaft torque and induction generator electromagnetic torque.

By lower whole wind energy conversion system rotating speed and torque angle at given wind speed, can make the mechanical output of wind energy conversion system output reach maximum, optimize the capturing efficiency of wind energy, conventionally to maximize the ratio of the wind power of wind energy conversion system power output and input, i.e. power factor C _prepresent C _pwith torque angle β and tip speed ratio λ (λ=ω _tr/V _w, V _wfor wind speed, R is blade radius) relation suc as formula shown in (4), mark λ wherein _ithe fixed function relation forming for substituting λ and β:

$\begin{array}{c}{C}_p=0.22(\frac{116}{{\mathrm{\λ}}_i}-0.4\mathrm{\β}-5)e^{\frac{-12.5}{{\mathrm{\λ}}_i}}\\ {\mathrm{\λ}}_i=\frac{1}{1/(\mathrm{\λ}+0.08\mathrm{\β})-0.035/({\mathrm{\β}}^3+1)}\end{array}---\left(4\right)$

Wind energy conversion system power output P _twith C _p, β, ω _tmeet following relation:

$P_t=\frac{1}{2}\·{\mathrm{\ρ}}_{\mathrm{air}}\·{\mathrm{\πR}}^5\·\frac{C_P}{{\mathrm{\λ}}^3}\·{\mathrm{\ω}}_t^3=K_t\·{\mathrm{\ω}}_t^3---\left(5\right)$

When wind energy conversion system is during in optimum wind energy trap state, K _tfor a constant relevant with wind energy conversion system external form, be designated as K _t.opt, meet:

$K_{t.\mathrm{opt}}=\frac{1}{2}\·{\mathrm{\ρ}}_{\mathrm{air}}\·{\mathrm{\πR}}^5\·\frac{C_{P.\mathrm{opt}}}{{\mathrm{\λ}}_{\mathrm{opt}}^3}---\left(6\right)$

Wherein, subscript opt represents that blower fan is in max power point tracking state.

Therefore,, by formula (6) substitution formula (5), through arranging, can obtain formula (7):

${\mathrm{\ω}}_{r.\mathrm{ref}}=\sqrt[3]{\frac{P_t}{K_{t.\mathrm{opt}}}}=\sqrt{\frac{T_t}{K_{t.\mathrm{opt}}}}---\left(7\right)$

According to the machine torque of blower fan, can calculate optimal Generator speed reference ω _r.ref, the wind energy capturing in this rotating speed leeward function is maximum.From formula (2) and formula (3), regulate stator and rotor electric current can change electromagnetic torque, reach the object of controlling rotating speed.

Under nominal situation, rotor-side converter (RSC) controller be take the synchronous rotary referential (the d axle that be rotor with the vector position of stator magnetic linkage identical) of stator magnetic linkage as guiding by adopting, can realize the decoupling zero of the meritorious and idle control of double-fed blower fan, be presented as relatively independent q axle and d axle control loop, as shown in Figure 2.Wherein, q axle is realized the control to electromagnetic torque, generally by the error of rotor speed or active power, is decided the size of electromagnetic torque; The control of the corresponding exciting current of d axle, the reactive power that the size of exciting current is exported by hope determines.

The control of grid side current transformer (GSC), equally based on vector control technology, be take stator magnetic linkage as reference system.Active power is responsible for controlling in d axle loop, to maintain the stable of DC-link voltage; Reactive power is responsible for controlling in q axle loop, as shown in Figure 3.According to node current law, DC-link voltage meets with the branch current that is connected:

$i_{\mathrm{os}}=i_{\mathrm{or}}+i_c=i_{\mathrm{or}}+C\frac{{\mathrm{du}}_{\mathrm{dc}}}{\mathrm{dt}}---\left(8\right)$

$i_{\mathrm{or}}=\frac{P_r}{u_{\mathrm{dc}}}---\left(9\right)$

$i_{\mathrm{dg}}=\frac{2\sqrt{2}}{\sqrt{3}m}\·i_{\mathrm{os}}---\left(10\right)$

Wherein, i _or, i _osand i _crepresent that respectively direct-current chain circuit connects the electric current (as shown in Figure 1) of three branch roads of rotor, net side and capacitor C, i _dgfor the direct axis component of grid side electric current, u _dcfor capacitor C both end voltage, P _rfor flow into the active power instantaneous value of direct-current chain from rotor-side converter, m is pulse width modulation (PWM) modulation depth (modulation depth), gets 0.75.

In order to reduce as far as possible the negative effect of large-scale wind power access to electric network reliability, many countries all network and have formulated low voltage crossing standard for blower fan.For the serious power grid accident of the aspects such as better defence voltage, frequency, traditional fired power generating unit, except being required to possess low voltage ride-through capability, also requires to have the ability that under the state of emergency, power supports.Along with wind-powered electricity generation permeability constantly increases, some countries have started further to require blower fan to provide reactive current under fault condition, to help electrical network recovery voltage as early as possible.For double-fed blower fan, realize safe low voltage crossing, need to solve the key technical problems such as rotor overcurrent, direct-current chain overvoltage and current transformer overload.

Yet the control method of existing double-fed blower fan reply low voltage crossing is roughly divided into crow bar protective circuit and demagnetization method two classes.Crow bar protective circuit is at present unique method that obtains engineering application, but it need to increase hardware investment, and increases cooling system burden when fault.When crow bar is controlled activation, double-fed blower fan changes induction generator into, can absorb a large amount of reactive powers, is unfavorable for the rapid recovery of line voltage.Demagnetization method is offset the transient current of inducting because of magnetic linkage by producing reverse current.Yet the common more complicated of these class methods, is limited by controller time lag to the negative effect of tracing process (may increase fault current peak value under extreme case), algorithm reliability is not high, thereby is difficult to obtain commercial Application.Meanwhile, above-mentioned two class methods all do not consider that under fault, blower fan provides the problem of reactive power support to electrical network.

Summary of the invention

The present invention seeks to: for overcoming the deficiency of the control method of existing double-fed blower fan reply low voltage crossing, provide a kind of temporary wind energy of injecting of rotor inertia of utilizing, realize the control method of double-fed wind power generator low voltage crossing and reactive power support simultaneously.The feature that the method is variable according to speed-changing draught fan rotor speed, application rotor inertia kinetic energy change amount and output electric energy summation equal to input the conservation of energy principle of wind energy, by the inner kinetic energy of double-fed blower fan under restriction grid failure state to the conversion of electric energy, to be limited energy is stored in rotor inertia energy temporarily, effectively reduce the basic amplitude of rotor current, to realize safe low voltage crossing; By the cascade reaction type reactive controller that adds to work all the time, coordinate the idle output of rotor-side and grid side current transformer, to improve the reactive power support of double-fed blower fan to electrical network under fault condition simultaneously.By detecting common connecting point place residual voltage and catching wind speed, automatic regulation controller parameter, so that above-mentioned control method can be applied to different wind speed, accident residual voltage scene.

Specifically, the present invention realizes by the following technical solutions, comprises the steps:

1) under nominal situation, adopt and take max power point tracking and as controlling the optimal wind energy capture control method of target, double-fed blower fan system is controlled;

2) after monitoring power grid accident, by the control loop of rotor-side converter originally by according to rotor speed measured value ω _rwith its reference value ω _r.refthe electromagnetic torque reference value T that provides of the proportional integral value of difference _e.refswitch to directly by expression formula provide, wherein, U _sfor common connecting point voltage effective value, U _s.ratedfor common connecting point voltage rating, K _t.optfor optimum gain mode value, τ is the Torque Control factor, 0≤τ≤1; In whole failure process, do not disconnect the electrical connection of current transformer and rotor circuit other parts;

In whole low voltage crossing process, reactive controller continuous firing; Described reactive controller comprises rotor-side converter controller and grid side inverter controller, by cascade reaction type, connects, and wherein, rotor-side converter controller adopts common connecting point voltage U _sand reference value U _s.refthe proportional integral value of difference as the idle reference value Q of rotor-side _s.ref, final reactive power is sent by stator side, Q _s.refcan not surpass stator side current transformer rated capacity; Q _s.refsend idle Q with stator side is actual _sdifference as the idle reference value Q of grid side inverter controller _g.ref, Q _g.refcan not surpass grid side current transformer rated capacity;

3) when reaching the minimum of GB/T 19963-2011 regulation, stay the net time, and when fault clearance voltage recovers or rotor speed surpasses maximum (top) speed, by the electromagnetic torque reference value T in the control loop of rotor-side converter _e.refswitch back by according to rotor speed measured value ω _rwith its reference value ω _r.refthe proportional integral value of difference provide, recover to adopt optimal wind energy capture control method to control double-fed blower fan system.

Technique scheme is further characterized in that: described K _t.optcalculate as follows:

$K_{t.\mathrm{opt}}=\frac{1}{2}\·{\mathrm{\ρ}}_{\mathrm{air}}\·{\mathrm{\πR}}^5\·\frac{C_{p.\mathrm{opt}}}{{\mathrm{\λ}}_{\mathrm{opt}}^3}$

Wherein, ρ _airfor atmospheric density, R is pneumatic equipment blades made radius, C _pfor energy efficiency coefficient, λ is tip speed ratio, and subscript opt represents that blower fan is in max power point tracking state.

Technique scheme is further characterized in that: the transient voltage dip process after electric network fault is occurred is called the voltage section of falling, fault is not removed to the metastable stage of front residual voltage and be called voltage stabilization section, fault clearance, voltage are recovered to normal process gradually and be called voltage recovery section, Torque Control factor τ is by the voltage section of falling, 2 different phases difference values of voltage stabilization section; At voltage, recover section by turn the maximum permissible value T of electromagnetic torque down temporarily _e.maxand T _e.minabsolute value to avoid recovery process overcurrent, progressively unnecessary rotor inertia can be converted into electric energy, security recovery energy balance.

Beneficial effect of the present invention is as follows: the present invention to the conversion of electric energy, is temporarily stored in excess energy in rotor inertia energy stator and rotor current in the time of can effectively reducing double-fed blower fan low voltage crossing by capturing wind energy in restriction electric network fault process; By monitoring common connecting point voltage, can near supply between age at failure, load in residual voltage and the suitable active power of output of rated voltage ratio, also can delay rotor and accelerate, extend blower fan and stay the net time.Utilize blower fan residual capacity, especially by step 2, suitably improve exciting current and to electrical network, send reactive power when voltage falls, near voltage stablizing common connecting point is had to positive effect.The method realizes by current transformer being applied control, and does not adopt any high pass, band to lead to or low pass filter, is still single order control system, and speed is exceedingly fast; Need not increase the burden of cooling system for double-fed blower fan adds new hardware, reduce investment outlay.

Accompanying drawing explanation

Fig. 1 is double-fed blower fan system schematic diagram.

Fig. 2 is the control principle drawing of blower fan rotor-side converter (RSC) while normally moving.

Fig. 3 is the control principle drawing of blower fan grid side current transformer (GSC) while normally moving.

Fig. 4 is the control principle drawing of voltage of the present invention rotor-side converter (RSC) while falling.

Fig. 5 is reactive controller schematic diagram.

Fig. 6 is the division schematic diagram of voltage accident evolution different phase.

Fig. 7 is the line chart of test macro.

Fig. 8 is crow bar protective circuit schematic diagram.

Fig. 9 is that voltage falls time strategy B rotor-side converter and controls schematic diagram.

Figure 10 is the networking requirement of typical wind generator low voltage crossing performance.

To be double-fed blower fan fall 50% at voltage to Figure 11, the emulation transient response track of control strategy A, B, C under 8m/s wind speed: (a) common connecting point voltage; (b) active power; (c) rotor current; (d) DC-link voltage; (e) grid side electric current; (f) rotor speed.

To be double-fed blower fan fall 50% at voltage to Figure 12, the emulation transient response track of control strategy A, B, C under 8m/s wind speed: (a) reactive power; (b) stator side reactive power; (c) grid side reactive power; (d) capacitive reactive power electric current.

To be double-fed blower fan fall 85% at voltage to Figure 13, the emulation transient response track of control strategy A, B, C under 13m/s wind speed: (a) common connecting point voltage; (b) active power; (c) rotor current; (d) DC-link voltage; (e) grid side electric current; (f) rotor speed.

To be double-fed blower fan fall 85% at voltage to Figure 14, the emulation transient response track of control strategy A, B, C under 13m/s wind speed: (a) reactive power; (b) capacitive reactive power electric current.

To be double-fed blower fan fall 100% at voltage to Figure 15, the emulation transient response track of control strategy A, B, C under 13m/s wind speed: (a) reactive power; (b) capacitive reactive power electric current.

In order to occur for different faults, double-fed blower fan constantly falls 85% at voltage to Figure 16, the rotor current under 13m/s wind speed.

Figure 17 is for when failure detection time postpones 10ms, and double-fed blower fan falls 85% at voltage, application strategy A (crow bar protection), C (the present invention) comparison of rotor current afterwards under 13m/s wind speed.

Embodiment

With reference to the accompanying drawings and in conjunction with example the present invention is described in further detail.

The inventive method is the improvement in MPPT method, still adopts MPPT method to control double-fed blower fan system under nominal situation, the visible Fig. 1 of concrete control loop, Fig. 2, Fig. 3.

After monitoring power grid accident, by the control loop of rotor-side converter originally by according to rotor speed measured value ω _rwith its reference value ω _r.refthe electromagnetic torque reference value T that provides of the proportional integral value of difference _e.refswitch to directly and provide by expression formula (11), as shown in Figure 4.

$T_{e.\mathrm{ref}}=\mathrm{\τ}\·\frac{U_s}{U_{s.\mathrm{rated}}}\·K_{t.\mathrm{opt}}\·{\mathrm{\ω}}_{r.\mathrm{ref}}^2---\left(11\right)$

Wherein, U _sfor common connecting point voltage effective value, U _s.ratedfor common connecting point voltage rating, K _t.optfor optimum gain mode value, τ is the Torque Control factor, 0≤τ≤1; In whole failure process, do not disconnect the electrical connection of current transformer and rotor circuit other parts.K _t.optcalculate as follows:

$K_{t.\mathrm{opt}}=\frac{1}{2}\·{\mathrm{\ρ}}_{\mathrm{air}}\·{\mathrm{\πR}}^5\·\frac{C_{p.\mathrm{opt}}}{{\mathrm{\λ}}_{\mathrm{opt}}^3}---\left(12\right)$

Wherein, ρ _airfor atmospheric density, R is pneumatic equipment blades made radius, C _pfor energy efficiency coefficient, λ is tip speed ratio, and subscript opt represents that blower fan is in max power point tracking state.

When reaching the minimum of GB/T 19963-2011 regulation, stay under net time prerequisite, and in meeting the following conditions during arbitrary condition, by the electromagnetic torque reference value T in the control loop of rotor-side converter _e.refswitch back by according to rotor speed measured value ω _rwith its reference value ω _r.refthe proportional integral value of difference provide, recover to adopt optimal wind energy capture control method to control double-fed blower fan system: 1. fault clearance, voltage recover; 2. rotor speed surpasses maximum (top) speed.

This control is intended to break double-fed blower fan nominal situation makes a bet into wind energy and the energy balance of sending electric energy, reduces the electrical power of sending, and under fault, the unnecessary wind energy of catching is temporary in rotor inertia energy, reaches the object that reduces rotor current basic value.

Particularly, when line voltage falls, the overall power output of double-fed blower fan declines thereupon, by loosening the constraint to rotor speed, turns down electromagnetic torque, can reduce the injection of mechanical output, recovers the power-balance under fault.As shown in Figure 2, reducing of electromagnetic torque, brings reducing of rotor q shaft current.From energy point of view, loosen rotating speed constraint and will bring the raising of rotating speed, the mechanical energy absorbing from wind energy then be stored in rotor the principle of similar flywheel energy storage.Disregard frictional dissipation, the mechanical energy that t stores is constantly relevant with incremental speed, meets following formula:

$E_t=\frac{1}{2}J({\mathrm{\ω}}_t^2-{\mathrm{\ω}}_{\mathrm{start}}^2)---\left(13\right)$

Wherein, ω _startwith ω _trepresent that respectively t moment rotor speed in the moment and fault occurs fault, J represents rotor inertia constant.Under high wind speed scene, loosening of rotating speed constraint can trigger the control of torque angle immediately, and restriction is caught wind energy, thereby final rotating speed is limited in below maximum permissible revolution, so this method is very little to the negative effect of blower fan safety.The energy of temporary transient storage can be sent into comparatively stably electrical network after Failure elimination, voltage recover in speed regulation process, need not control separately.

For avoiding overcurrent, by formula (7), easily released the maximum power that allows to inject generator between age at failure, it is determined by grid residual voltage and optimized rotating speed reference value:

$P_{t.}\≤\frac{U_s}{U_{s.\mathrm{rated}}}\·K_{t.\mathrm{opt}}\·{\mathrm{\ω}}_{r.\mathrm{ref}}^3---\left(14\right)$

Between q axle rotor current reference value and electromagnetic torque reference value, meet the relation of formula (15):

$i_{\mathrm{qr}.\mathrm{ref}}=-\frac{L_s}{L_m{\mathrm{\ψ}}_s}\·T_{e.\mathrm{ref}}---\left(15\right)$

Wherein, i _qr.reffor q axle rotor current reference value, L _sfor stator inductance, L _mfor mutual inductance, Ψ _sfor stator magnetic linkage.Stator magnetic linkage Ψ _sbecause changing rapidly and not accepting direct control, be difficult to Measurement accuracy, cause inaccurate reference value setting and cause controlling error.I _qr.refabout Ψ _ssingle order partial derivative be,

$\frac{{\∂i}_{\mathrm{qr}.\mathrm{ref}}}{{\∂\mathrm{\Ψ}}_s}=\frac{L_s}{L_m{\mathrm{\Ψ}}_s^2}\·T_{e.\mathrm{ref}}---\left(16\right)$

From formula (16), reduce stator magnetic linkage Ψ _sthe impact of measure error can be by reducing electromagnetic torque reference value T _e.refvalue realize, simultaneously from energy viewpoint, the transfer process of double-fed blower fan inside from mechanical energy and magnetic field energy to electric energy is also because of T _e.refturned down, and be delayed.Consideration formula (14), when low voltage crossing, electromagnetic torque reference value can be given by formula (17):

$T_{e.\mathrm{ref}}=\mathrm{\τ}\·\frac{U_s}{U_{s.\mathrm{rated}}}\·K_{t.\mathrm{opt}}\·{\mathrm{\ω}}_{r.\mathrm{ref}}^2,0\≤\mathrm{\τ}\≤1---\left(17\right)$

The τ factor, for effectively suppressing the current spike of the voltage section of falling rotor, is guaranteed safe low voltage crossing.Transient voltage dip process after electric network fault is occurred is called the voltage section of falling; Fault is not removed to the metastable stage of front residual voltage and be called voltage stabilization section; Fault clearance, voltage are recovered to normal process gradually and be called voltage recovery section, the division in 3 stages as shown in Figure 6.τ can be by the voltage section of falling, 2 different phases difference values of voltage stabilization section.

As larger τ can increase rotor current, generally in the voltage section of falling, get 0-0.5; In voltage stabilization section, the too small value of τ may make the too fast increase of rotor speed, especially, under the longer scene of high wind speed, trouble duration, generally with capping value 0.5, is advisable.At voltage, recover section by turn the maximum permissible value T of electromagnetic torque down temporarily _e.maxand T _e.minabsolute value to avoid recovery process overcurrent, progressively unnecessary rotor inertia can be converted into electric energy, security recovery energy balance.Turn strategy temporarily down and trigger when voltage being detected and recover, rule of thumb or emulation experiment determine T _e.maxand T _e.minthe adjusting range of absolute value, the desirable 0.1-0.3 of typical adjustment amount (perunit value).Concrete setting (the T in this embodiment that can see below described in tactful C _e.minabsolute value be adjusted to 1.2 perunit values).

For reactive power support is provided, in whole low voltage crossing process, reactive controller continuous firing.Reactive controller comprises rotor-side converter controller and grid side inverter controller, by cascade reaction type, connect, as shown in Figure 5, in Fig. 5, " rotor-side converter controller " is control loop shown in Fig. 2 (being Fig. 4 during electric network fault), and " grid side inverter controller " is control loop shown in Fig. 3; In Fig. 5, signal branch is connected with branch road of the same name in Fig. 2-Fig. 4.Wherein, rotor-side converter controller adopts common connecting point voltage U _sand reference value U _s.refthe proportional integral value of difference as the idle reference value Q of rotor-side _s.ref, due to finally via stator side output reactive power, therefore Q _s.refcan not surpass stator side current transformer rated capacity; Q _s.refsend idle Q with stator side is actual _sdifference as the idle reference value Q of grid side inverter controller _g.ref, Q _g.refcan not surpass grid side current transformer rated capacity.

This control mode makes the reactive power under normal or fault condition automatically distribute and (preferentially output reactive power be distributed to RSC in both sides; when not enough, use GSC to send reactive power); while reaching nominal situation, grid side is idle is output as zero, the control effect that the rotor-side of take during fault is exported as main, both sides simultaneously.Reactive power output total amount is provided by the proportional integral device that reflects common connecting point voltage control error, realizes Voltage Feedback and controls.

Control effect of the present invention can embodied on single system as shown in Figure 7, and this embodiment has compared 3 kinds of typical control strategies, falls in scene its low voltage crossing of high spot reviews and reactive power support ability at different voltage.These 3 kinds of strategies are respectively:

Strategy A: install the control strategy of crowbar circuit additional, as shown in Figure 8.Crow bar resistance is made as 40 times of rotor resistances, and the threshold value of rotor and stator current starting protection is all made as to 1.5 times of rated current;

Strategy B: magnetic linkage Tracking Control Strategy (as shown in Figure 9, grid side adopts the control strategy of Fig. 3 to the control strategy of rotor-side when voltage falls all the time);

Strategy C: the control strategy that the present invention proposes, relevant controlling parameters arranges as follows:

For the ease of comparing, tactful A has also applied the idle control strategy identical with the present invention with C, and rotor protection starting method is all identical with tactful B with threshold value, and stator and rotor current starts after arriving 1.5 times of rated current.Simulating scenes, according to the most harsh situation of Figure 10, extracts typical 3 scenes, by voltage fall degree, minimum stays net time (ms of unit) two tuples to be described as: (0.50,1733), (0.85,625), (1,150).

Simulation result below.

At voltage, fall 50%, under duration 1733ms, low wind speed (wind speed is 8m/s) scene, apply respectively 3 kinds of control strategies and implement the control to blower fan, the time domain transient response curve of its major parameter as shown in figure 11.3 kinds of strategies under this fault condition, all can meet rotor, stator transient current lower than 2 times of rated values, current on line side lower than 1.5 times of rated values, DC-link voltage amplification lower than 15%, Converter Capacity is lower than the requirement of 0.3 times of rated value.Because tactful C recovers the control that section discharges inertia energy, rotor current peak value obviously reduces.Aspect power stage, the active power that tactful C exports between age at failure surpasses 0.1 times of rated value; Strategy A makes double-fed blower fan change induction generator into, when voltage falls, from electrical network, absorbs active power.Because sending the difference of active power, tactful C has obviously suppressed the increase of rotating speed, as shown in Figure 11 (f).As induction motor, strategy A between age at failure from electrical network absorbing reactive power, strategy B and C send the reactive power that is equivalent to 50% rated capacity from stator side to electrical network by powerless control method of the present invention, the capacitive reactive power electric current that is equivalent to 100% rated value is provided altogether.As shown in Figure 12 (a), the reactive power that tactful A can provide is much less.

At voltage, fall 85%, under duration 625ms, high wind speed (wind speed is 13m/s) scene, rotor current vibration obviously increases, and as shown in Figure 13 (c), causes rotor, GSC side electric current, DC-link voltage to raise.At voltage, recover section, the more tactful A of rotor current, the B of tactful C are lower, more level and smooth.The reactive current that strategy C sends to electrical network is more than 1.5 times, as shown in figure 14 of tactful A, B.

Figure 15 shows that common connecting point voltage drops at 0 o'clock, the rotor of double-fed blower fan and reactive current.Strategy C, under the prerequisite of the minimum rotor current peak value of maintenance, provides average the highest reactive current.

Aspect algorithm robustness, Figure 16 show fault occur constantly to delay 1/4 and half cycle situation under the time-domain curve of double-fed fan rotor electric current under control strategy that the present invention carries control.As seen from the figure, 3 curves have high similarity.

Figure 17 has compared when voltage falls to detect and has postponed in 10ms situation, and crow bar is controlled the rotor current time-domain curve of (tactful A) and strategy that the present invention carries (tactful C).As seen from the figure, the unavoidable appearance of current peak occurring in the voltage section of falling increases, but both increasing degrees are in same level.

Although the present invention with preferred embodiment openly as above, embodiment is not of the present invention for limiting.Without departing from the spirit and scope of the invention, any equivalence of doing changes or retouching, belongs to equally the present invention's protection range.Therefore should to take the application's the content that claim was defined be standard to protection scope of the present invention.

Claims (3)

1. the double-fed blower fan low voltage crossing of buffer memory wind energy and a reactive power support control method, is characterized in that, comprises the following steps:

1) under nominal situation, adopt and take max power point tracking and as controlling the optimal wind energy capture control method of target, double-fed blower fan system is controlled;

2) after monitoring power grid accident, by the control loop of rotor-side converter originally by according to rotor speed measured value ω _rwith its reference value ω _r.refthe electromagnetic torque reference value T that provides of the proportional integral value of difference _e.refswitch to directly by expression formula provide, wherein, U _sfor common connecting point voltage effective value, U _s.ratedfor common connecting point voltage rating, K _t.optfor optimum gain mode value, τ is the Torque Control factor, 0≤τ≤1; In whole failure process, do not disconnect the electrical connection of current transformer and rotor circuit other parts;

In whole low voltage crossing process, reactive controller continuous firing; Described reactive controller comprises rotor-side converter controller and grid side inverter controller, by cascade reaction type, connects, and wherein, rotor-side converter controller adopts common connecting point voltage U _sand reference value U _s.refthe proportional integral value of difference as the idle reference value Q of rotor-side _s.rdf, final reactive power is sent by stator side, Q _s.refcan not surpass stator side current transformer rated capacity; Q _s.refsend idle Q with stator side is actual _sdifference as the idle reference value Q of grid side inverter controller _g.ref, Q _g.refcan not surpass grid side current transformer rated capacity;

3) when reaching the minimum of GB/T 19963-2011 regulation, stay the net time, and when fault clearance voltage recovers or rotor speed surpasses maximum (top) speed, by the electromagnetic torque reference value T in the control loop of rotor-side converter _e.refswitch back by according to rotor speed measured value ω _rwith its reference value ω _r.refthe proportional integral value of difference provide, recover to adopt optimal wind energy capture control method to control double-fed blower fan system.

2. the double-fed blower fan low voltage crossing of buffer memory wind energy according to claim 1 and reactive power support control method, is characterized in that, described K _t.optcalculate as follows:

$K_{t.\mathrm{opt}}=\frac{1}{2}\·{\mathrm{\ρ}}_{\mathrm{air}}\·{\mathrm{\πR}}^5\·\frac{C_{p.\mathrm{opt}}}{{\mathrm{\λ}}_{\mathrm{opt}}^3}$

Wherein, ρ _airfor atmospheric density, R is pneumatic equipment blades made radius, C _pfor energy efficiency coefficient, λ is tip speed ratio, and subscript opt represents that blower fan is in max power point tracking state.

3. the double-fed blower fan low voltage crossing of buffer memory wind energy according to claim 1 and reactive power support control method, it is characterized in that, transient voltage dip process after electric network fault is occurred is called the voltage section of falling, fault is not removed to the metastable stage of front residual voltage and be called voltage stabilization section, fault clearance, voltage are recovered to normal process gradually and be called voltage recovery section, Torque Control factor τ is by the voltage section of falling, 2 different phases difference values of voltage stabilization section; At voltage, recover section by turn the maximum permissible value T of electromagnetic torque down temporarily _e.maxand T _e.minabsolute value to avoid recovery process overcurrent, progressively unnecessary rotor inertia can be converted into electric energy, security recovery energy balance.