CN102624029B - Topological structure specific to low voltage ride through for doubly-fed type wind power generation system - Google Patents

Abstract

The invention provides a topology specific to low voltage ride through for a doubly-fed type wind power generation system. By means of series connection of electric reactors on a rotor side converter and a rotor port, impedance of a rotor return circuit of the system is improved. Due to the fact that in a normal condition, the current frequency of the rotor return circuit is power frequency which is times of slip rate, the impedance of series connection of the electric reactors is not large, while during faults of a power grid, high voltage sensed by a stator direct current magnetic chain and a negative sequence magnetic chain is respectively close to the power frequency and two times of the power frequency. At the moment, the electric reactors in series connection under corresponding frequency have high impedance so as to effectively suppress large current during a fault period, enable the converter to keep operating during the fault period and meet the requirement for lower voltage ride through.

Description

Double-fed type wind generator system is for a kind of topological structure of low voltage crossing

[technical field]

The present invention relates to new forms of energy (wind-power electricity generation) research field, particularly the topological structure that requires for low voltage crossing of double-fed type wind generator system.

[background technology]

Since the seventies in last century, the energy and environmental protection become one of focus that world pays close attention to gradually.Along with the continuous increase of energy resource consumption and the continuous minimizing of traditional energy thereof, the development of new forms of energy causes extensive concern and the promotion of the whole society, wherein wind-power electricity generation because of for ease of on a large scale utilize and lower cost obtain swift and violent development in recent years.Double-fed type wind generator system is selected due to the main flow that its variable-ratio runs, active reactive can control separately and the plurality of advantages of low Converter Capacity becomes in wind generator system.

But because the stator of double-fed type wind generator system is directly connected to electrical network, this kind wind generator system is very responsive to electric network fault.Line voltage to fall and recovery process can produce DC component in double feedback electric engine stator magnetic linkage in symmetry; this direct current magnetic linkage relative stator is static, with nearly synchronous speed cutting rotor; high voltage is induced at rotor-end mouth; make net side converter saturated, even exceed its rated voltage and cause its protection or puncture.Under asymmetric fault, also can produce negative phase-sequence magnetic linkage in stator magnetic linkage, this component relative stator is with synchronous speed counter-rotating, with nearly twice synchronous speed high-speed cutting rotor, induce higher voltage at rotor-end mouth, cause larger threat to rotor-side converter.Therefore under electric network fault; traditional way is to protect equipment of itself by out of service for current transformer; but because wind generator system proportion in power system is increasing; its excision can cause larger impact to power system; therefore power operation corporate policy meet certain fault apparatus for lower wind electricity generation system must keep networking; even provide idle to support line voltage to electrical network, i.e. low voltage crossing requirement.

By searching document, the Study on Problems personnel for double-fed type wind generator system low voltage crossing give following solution: by switch motion that is in parallel with impedance network or that connect by impedance network parallel connection or be connected on pusher side current transformer port to protect wind generator system.

As adopted the impedance network of parallel connection type, then current transformer is out of service between age at failure, the mode operation of double-fed type wind generator system traditionally asynchronous machine between age at failure, absorb from electrical network a large amount of idle, and need when power system restoration subsynchronous again, control comparatively complicated; As adopt the impedance network of tandem type then current transformer can keep between age at failure run, but the input of impedance network and excision can impact current transformer, and the optimum impedance difference needed under the different faults degree of depth, the design of impedance network there is no quantitative conclusion.

Below provide the pertinent literature of retrieval:

1. Wang Wei, Sun Mingdong, Zhu Xiaodong. double-feedback aerogenerator low voltage crossing technical Analysis. Automation of Electric Systems .2007,31 (23): 84-89.

2. to greatly, Yang Shunchang, Ran Li. the double fed induction generators system emulation research that runs of off-grid during electrical network symmetric fault. electrical engineering journal .2006.26 (10): 130-135.

3. He Yi, Kang Zhoupeng. speed variant frequency constant dual feedback asynchronous wind generator system low voltage crossing technology summary. electrotechnics journal .2009.24 (9): 140-146.

4. Su Ping, opens by society. dual feedback wind power generation system LVRT simulation study .2010.38 (23) based on active 1GBT type Crowbar: 164-171.

5.Jin YangJohn，E.Fletcher and John O’Reilly，“A Series Dynamic Resistor Based Converter Protection Scheme for Doubly-Fed Induction Generator During Various Fault Conditions，”IEEE TRANSACTIONS ON ENERGY CONVERSION，VOL.25，NO.2，pp.422-432，JUNE2010.

6.Iker Esandi，Xabier Juankorena，Jesús López and Luis MarroyoJ，“Alternative Protection System for Wind Turbines with Doubly Fed Induction Generator，”International Conference on Power Engineering，Energy and Electrical Drives，pp.501-506，May.2008.

7.M.Rahimi and M.Parniani，“Efficient control scheme of wind turbines with doubly fed induction generators for low voltage ride-through capability enhancement，”Renewable Power Generation，IET，vol.4，no.3，pp.242-252，May.2010.

[summary of the invention]

For the defect that above-mentioned existing Theory and technology exists or deficiency, the object of the invention is to propose the topological structure that a kind of double-fed type wind generator system is applicable to low voltage crossing, the rotor current between age at failure effectively can be suppressed by current-limiting reactor between pusher side current transformer and rotor port, keep the continuous firing of current transformer, can be good at meeting low voltage crossing requirement.

To achieve these goals, the present invention adopts following technical scheme:

Double-fed type wind generator system, for an a kind of topological structure for low voltage crossing, comprises double-feedback aerogenerator and rotor-side converter; Reactor is in series with between the rotor port of double-feedback aerogenerator and rotor-side converter.

The present invention further improves and is: described reactor none-disk terminal switch.

The present invention further improves and is: described topological structure also comprises a net side converter; Described net side converter connection rotor-side converter and rotor-side converter form electric current device back-to-back and are connected between the rotor port of double-feedback aerogenerator and electrical network.

The present invention further improves and is: the impedance of reactor under power frequency is 0.2Z _nto 2Z _n, wherein Z _nfor mark one impedance of double-fed type wind generator system; Z _n=V _sn/ I _sn, wherein V _sn, I _snbe respectively double-feedback type wind generator system stator rated voltage, stator rated current.

The present invention gives the topological structure of a kind of double-fed type wind generator system for low voltage crossing, tandem reactor between rotor port and pusher side current transformer.

Compared with prior art, the present invention has following beneficial effect: the present invention utilizes reactor to show the characteristic of different impedance at different frequencies, between double fed electric machine rotor port and pusher side current transformer, seal in reactor.For the high frequency voltage that stator DC magnetic linkage between age at failure and negative phase-sequence magnetic linkage induce at rotor-end mouth, current-limiting reactor shows high impedance, thus the effective electric current suppressed in rotor loop, keep the continuous operation of current transformer, realize low voltage crossing requirement.

[accompanying drawing explanation]

Fig. 1 is double-fed type wind generator system conventional topologies structure chart;

Fig. 2 is rotor loop equivalent circuit diagram;

Fig. 3 is double-fed type wind generator system stator voltage and rotor induction pressure under the symmetrical electric network fault of the degree of depth 85%;

Fig. 4 be double-fed type wind generator system under conventional topologies continue 0.625 second, the stator current under the symmetrical electric network fault of the degree of depth 85%, rotor current response;

Fig. 5 be in the present invention double-fed type wind generator system for the topology diagram of low voltage crossing;

Fig. 6 be in the present invention under topological structure double-fed type wind generator system pin continue 0.625 second, the stator current under the symmetrical electric network fault of the degree of depth 85%, rotor current response.

[detailed description of the invention]

Below in conjunction with accompanying drawing, the present invention is described in further detail.

With reference to Fig. 1, typical double-fed wind power generator group comprises wind energy conversion system, gear-box, double-fed type motor, back-to-back converter and three winding step-up transformer.Because current transformer only processes slippage rated power doubly, so its cost, volume, loss contrast and total power converter are all lower, be therefore used widely in wind generator system.But being directly connected to electrical network due to the stator of double-feedback aerogenerator, electric network fault can be passed to rotor current transformer by the coupling of motor stator rotor, thus causes very large threat to motor.

Stator magnetic linkage under normal condition expression formula such as formula 1:

${\stackrel{\→}{\mathrm{\ψ}}}_s\left(t\right)=\frac{V_s}{j{\mathrm{\ω}}_s}{e}^{j{\mathrm{\ω}}_{s}t}---\left(1\right)$

Wherein V _sline voltage, ω _sit is synchronous rotary angular frequency; J represents phase angular advance 90 °.This stator magnetic linkage relative stator is with synchro angle frequencies omega _srotate, relative rotor is with slip angular frequency s ω _srotate, the induced electromotive force expression formula produced in the rotor is such as formula 2:

${\stackrel{\→}{V}}_r\left(t\right)=s{V}_s{e}^{\mathrm{js}{\mathrm{\ω}}_{s}t}---\left(2\right)$

Wherein s is revolutional slip, and span is-0.3-0.3.

Under symmetrical electric network fault, in stator magnetic linkage, DC component can be induced

${\stackrel{\→}{\mathrm{\ψ}}}_{\mathrm{sn}}\left(t\right)=\frac{{\mathrm{PV}}_s}{{\mathrm{j\ω}}_s}{e}^{j{\mathrm{\ω}}_s{t}_0}{e}^{-\frac{\mathrm{\τ}}{t}}(t\≥t_0)---\left(3\right)$

Wherein P is the fault degree of depth, t ₀for fault initial time, τ is stator time constant.Stator DC magnetic linkage relative stator is static, and relative rotor is with (1-s) ω _sangular frequency rotates, and thus induces the component of high-frequency and high-voltage at rotor-end mouth

${\stackrel{\→}{V}}_{r\_n}\left(t\right)=-(1-s){\mathrm{PV}}_s{e}^{-j(1-s){\mathrm{\ω}}_{s}t}---\left(4\right)$

Under asymmetric fault, in stator magnetic linkage, also comprise negative sequence component

${\stackrel{\→}{\mathrm{\ψ}}}_{\mathrm{neg}}\left(t\right)=\frac{V_{s\_\mathrm{neg}}}{-j{\mathrm{\ω}}_s}{e}^{-j{\mathrm{\ω}}_{s}t}(t\≥t_0)---\left(5\right)$

V _{s_neg}represent stator negative sequence voltage virtual value.Stator negative phase-sequence magnetic linkage relative stator is with synchronous rotary angular frequency _srotate, relative rotor is then with (2-s) ω _sangular frequency rotates.Thus the component of more high frequency is induced at rotor-end mouth

${\stackrel{\→}{V}}_{r\_\mathrm{neg}}\left(t\right)=-(2-s)V_{s\_\mathrm{neg}}{e}^{-j(2-s){\mathrm{\ω}}_{s}t}---\left(6\right)$

Contrast equation (2) (4) (6) can draw, during electric network fault, stator magnetic linkage induces the voltage of high frequency amplitude in rotor port, when under symmetric fault, line voltage falls to zero, induced voltage can reach the 4-6 of rated voltage doubly.During electric network fault, the equivalent circuit of rotor loop as shown in Figure 2.Because rotor loop equivalent resistance is very little, when rotor-end mouth induced electromotive force is much larger than the rated voltage of rotor-side converter, both pressure reduction can produce huge electric current in rotor loop, thus forces current transformer out of service, even damages current transformer.At s=0.3, the symmetric fault lower rotor part induction voltage waveform figure of P=0.85 as shown in Figure 3, visible induced electromotive force is far above pusher side current transformer rated voltage, the response of now fully loaded traditional double-feedback aerogenerator as shown in Figure 4, visible fault causes very high electric current at rotor loop, far above the rated current of pusher side current transformer.

The present invention proposes a kind of topological structure of a kind of double-fed type wind generator system for low voltage crossing, as shown in Figure 5, namely on the basis of conventional topologies, extra reactor is added, be series between pusher side current transformer (rotor-side converter) and rotor, the characteristic utilizing the impedance of reactor to be directly proportional to frequency suppresses the Transient Currents between age at failure, to ensure the continuous service of current transformer.Make a concrete analysis of as follows:

The impedance magnitude of current-limiting reactor can be expressed as:

$Z_{L_{\mathrm{series}}}\left(\mathrm{\ω}\right)=\mathrm{\ω}{L}_{\mathrm{series}}---\left(7\right)$

Wherein ω is angular frequency, L _seriesfor inductance size.In normal conditions, the electric current of rotor loop only containing revolutional slip times power frequency, namely frequency is s ω _s, be s ω by the impedance magnitude of (7) known current-limiting reactor under this frequency _sl _series; For the induced electromotive force that stator DC magnetic linkage under fault causes at rotor loop, know that its frequency is for (1-s) ω by (4) _s, then the impedance magnitude that current-limiting reactor shows under this frequency is (1-s) ω _sl _series; For the induced electromotive force that stator negative phase-sequence magnetic linkage between age at failure causes at rotor loop, know that its frequency is for (2-s) ω by (6) _s, then the impedance magnitude that current-limiting reactor shows under this frequency is (2-s) ω _sl _series.

From analyzing above, under normal circumstances, the ammeter of current-limiting reactor to rotor loop reveals Low ESR, under nonserviceabling, high resistant is shown as to the frequency at fault current place, thus effectively inhibit the current amplitude of rotor loop between age at failure, ensure that the normal work of current transformer, realize low voltage crossing.

Current-limiting reactor design considerations of the present invention is that rotor loop electric current is no more than setting (representative value is 1.5 to 2 times of rotor rated current) between age at failure.Under different low voltage crossing specifications, DC voltage value, Converter Capacity and electric machine rotor turn ratio condition, the impedance span of current-limiting reactor under power frequency is 0.2Z _n-2Z _n, wherein Z _nfor mark one impedance of double-fed type wind generator system, its computing formula is Z _n=V _sn/ I _sn, wherein V _sn, I _snbe respectively system stator rated voltage, stator rated current.

The response of the double-fed type wind generator system topological structure that the present invention proposes under the symmetric fault of s=0.3, P=0.85 as shown in Figure 6.Can see that between age at failure, rotor current is effectively limited within twice rated current, this can allow during short trouble.

The topological structure of a kind of double-fed type wind generator system for low voltage crossing is given in the present invention, this topology realizes low voltage crossing by increasing current-limiting reactor before rotor port and rotor-side converter, and does not need special control method and hardware action.Can see from the result of emulation, this topology can be good at suppressing the transient current between age at failure, keeps current transformer continuous firing between age at failure, realizes low voltage crossing.

Claims (1)

1. double-fed type wind generator system is for a kind of topological structure of low voltage crossing, it is characterized in that, comprises double-feedback aerogenerator and rotor-side converter; Reactor is in series with between the rotor port of double-feedback aerogenerator and rotor-side converter; Described reactor none-disk terminal switch; The impedance of reactor under power frequency is 0.2Z _nto 2Z _n, wherein Z _nfor mark one impedance of double-fed type wind generator system; Z _n=V _sni _sn, wherein V _sn, I _snbe respectively double-feedback type wind generator system stator rated voltage, stator rated current; Described topological structure also comprises a net side converter; Described net side converter connection rotor-side converter and rotor-side converter form electric current device back-to-back and are connected between the rotor port of double-feedback aerogenerator and electrical network; Under normal circumstances, the ammeter of current-limiting reactor to rotor loop reveals Low ESR, under nonserviceabling, high resistant is shown as to the frequency at fault current place, effectively inhibit the current amplitude of rotor loop between age at failure, ensure that the normal work of current transformer, realize low voltage crossing.