CN102148492B - Method for acquiring control input signal of subsynchronous oscillation suppression and control device - Google Patents

Abstract

The invention relates to a method for acquiring a control input signal of a subsynchronous oscillation suppression and control device. In the method, a three-phase AC bus voltage Vabc(t) of an access point of the subsynchronous oscillation suppression and control device serves as an input voltage signal which is converted into two phases of orthogonal static coordinate signals Valpha(t) and Vbeta(t) by Clarke conversion, and a phase error signal Pherr is output after the two phases of orthogonal static coordinate signals pass through a digital phase closed loop link; and a generator set shafting torsional vibration mode signal is separated from the phase error signal by a filtering link as the control input signal of the subsynchronous oscillation suppression and control device. In the method, the bus AC voltage of the access point of the subsynchronous oscillation suppression and control device is adopted as a source signal, and the generator set shafting torsional vibration mode signal is obtained by digital phase locked loop and digital processing technologies, and the reliable control input signal can be provided in situ for a device; and the method is relatively lower in cost and easy to implement.

Description

The acquisition methods of a kind of sub-synchronous oscillation inhibition and protective device control inputs signal

Technical field

The invention belongs to field of power, be specifically related to the acquisition methods of a kind of sub-synchronous oscillation inhibition and protective device control inputs signal.

Background technology

Sub-synchronous oscillation, is a kind of transient process of a kind of electrical network and steam turbine positive energy exchange in one or several frequency lower than power frequency, and the energy exchange of this vibration may be underdamping or negative damping, if negative damping is unsettled.China's Thermal Power Bases generally adopts a little to net Transmission Mode at present, transmission distance is generally longer, for the stability limit that improves circuit increases ability to transmit electricity, adopt series compensation technology of transmission of electricity and high voltage dc transmission technology, the application of Series Compensation and high voltage dc transmission technology all may cause that many fired power generating unit of sending end face sub-synchronous oscillation problem.If taking braking measure for every unit near machine is distolateral, project cost is high and control complicatedly, thereby need to adopt multiple inhibition and safeguard measure to solve the sub-synchronous oscillation problem of Thermal Power Bases multimachine in grid side.

The length of thermal power plant Steam Turbine Generator group rotor may exceed 40 meters, weight can reach hundreds of ton, each section of rotor can be regarded the lumped mass piece that some elasticity connects as, in disturbed axle system, each mass is in synchronous rotary, also can there is torsional oscillation vibration relative between mass, comprised a series of torsional modes, torsion frequency is called sub-synchronous oscillation lower than the synchronizing frequency of electrical network.Practical power systems is in dynamic balance state, and system disturbance all may cause the subsynchronous oscillation oscillatory occurences of the different amplitudes of shaft system of unit.Shaft system of unit is because its axle of the reason such as bearing friction, windage is that mechanical system presents positive damping feature, if mend device, high voltage dc transmission technology etc. without string in unit transmitting system, general and axle is that the subsynchronous hunting of frequency of subsynchronous oscillation frequency complementary is positive damping feature in electrical network, disturbance causes that the subsynchronous oscillation vibration of shaft system of unit presents positive damping characteristic, and oscillation amplitude decays very soon.In order to improve ability to transmit electricity and efficiency, thermal power plant transmitting system adopts string to mend device or high voltage dc transmission technology etc., sub-synchronous oscillation problem, generator rotor shaft system torsional oscillation problem or the generation axle lasting or even amplification that may cause electric power system are fatigue loss, in serious situation, can cause shaft system of unit damage accident.

Thermal power plant Steam Turbine Generator group rotor is made up of steam turbine section and generator section, steam turbine section is made up of each section of high pressure cylinder, intermediate pressure cylinder and low pressure (LP) cylinder, generator section or contain exciter, as shown in Figure 1, longer elastic shaft system of each section of composition, in figure, 1 is steam turbine high-pressure cylinder, 2 is low pressure (LP) cylinder A, 3 is low pressure (LP) cylinder B, and 4 is generator.When the electric power system generation disturbance of generator connecting in parallel with system, can cause the variation of generator electromotive power output, cause that it is electromagnetic torque disturbance that generator is applied to axle.Shaft system of unit, as longer elastic system, produces mutual torsional oscillation vibration between each section when disturbed, there be N-1 torsional oscillation mode in a N section axle system, and part model frequency is lower than synchronized frequency.If with the subsynchronous hunting of frequency of shafting torsional oscillation mode frequency complementary in electrical network, be non-positive damping feature, disturbance causes that the subsynchronous oscillation vibration of shaft system of unit presents non-positive damping characteristic, the vibration of axle system maintains compared with large amplitude or increasing oscillation, and causing axle is fatigue loss or damage.

Sub-synchronous oscillation problem becomes a safe operation major issue that jeopardizes electrical network.At present sub-synchronous oscillation problem is had to multiple braking measure and safeguard measure.To near the sub-synchronous oscillation braking measure of unit as supplementary excitation damping control, dynamic stability device etc., protective device as axle be torsional stress relay and armature supply relay etc., pass through photoelectric tachometric transducer, Hall revolution speed transducer or as shown in Figure 1 magnetoelectric tachometric transducer, 5-tachometric survey gear in Fig. 1, 6-gear emboss pit, 7 is induction coil, 8 is permanent magnet, 9 is air gap, 10 is magnetic conductive soft iron, 11 is signal conditioning circuit, be the signal of telecommunication that rotating speed is converted to alternation axle, this signal is by extremely device of cable transmission, by filtering, signal condition and employing change digital signal into, be decomposed into torsional oscillation mode signal through Digital Signal Processing again, as the input signal of controller.

China's Thermal Power Bases generally adopts a little to net Transmission Mode at present, transmission distance is generally longer, for the stability limit that improves circuit increases ability to transmit electricity, adopt series compensation technology of transmission of electricity and high voltage dc transmission technology, the application of Series Compensation and high voltage dc transmission technology all may cause that many fired power generating unit of sending end face sub-synchronous oscillation problem.If taking braking measure for every unit near machine is distolateral, project cost is high and control complicatedly, thereby need to adopt multiple inhibition and safeguard measure to solve the sub-synchronous oscillation problem of Thermal Power Bases multimachine in grid side.Unit rotor speed measuring-signal is to suppress and the reliable input signal of protective device near machine end sub-synchronous oscillation; and to having the grid side sub-synchronous oscillation of certain distance to suppress and protective device with unit; if adopt unit rotor speed signal as input signal; possible Problems: the axle of multiple units is that tach signal all needs by certain distance traffic channel to suppressing and protective device, and the higher and intermediate link of engineering cost reduces the reliability of engineering more.Based on this, exigence those skilled in the art develop the method for measurement of a sub-synchronous oscillation signal that can overcome above-mentioned defect.

Summary of the invention

In order to overcome the above-mentioned defect of prior art; the object of the invention is to propose that a kind of sub-synchronous oscillation suppresses and the acquisition methods of protective device control inputs signal, the cost of the method is lower, be easy to realize and can be on the spot provide reliable control inputs signal for sub-synchronous oscillation inhibition and protective device.

For achieving the above object, the acquisition methods of sub-synchronous oscillation inhibition of the present invention and protective device control inputs signal, is achieved through the following technical solutions:

An acquisition methods for sub-synchronous oscillation inhibition and protective device control inputs signal, its improvements are: the method is with the three-phase alternating current busbar voltage V of sub-synchronous oscillation inhibition and protective device access point _abc(t), as input voltage signal, this input voltage signal is transformed to the orthogonal static coordinate signal of two-phase V through Clarke _α(t), V _β(t), the orthogonal static coordinate signal of two-phase V _αand V (t) _β(t) through digital phase-locked loop link output phase error signal Ph _err; Phase error signal Ph _errlink is isolated the control inputs signal of generator set torsional vibration mode signal as sub-synchronous oscillation inhibition and protective device after filtering.

Wherein, described digital phase-locked loop link comprises ratio-integral element, integral element and feedback element, and its concrete steps are as follows:

If synchronized frequency is f ₀=50Hz, synchronous phase angle is β=ω ₀t=2 π f ₀t, three-phase alternating current busbar voltage is:

$\left\{\begin{array}{c}{v}_a=V_m\sin \left(\mathrm{\β}\right)\\ v_b=V_m\sin (\mathrm{\β}-\frac{2\mathrm{\π}}{3})\\ v_c=V_m\sin (\mathrm{\β}+\frac{2\mathrm{\π}}{3})\end{array}\right.$

Represent by vector form: v _abc=[v _av _bv _c] ^t

C is Clarke Clarke transformation matrix, C ^-1for inverse-transform matrix:

$C=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right]$ $C^{-1}=\left[\begin{array}{ccc}1& -\frac{1}{2}& 1\\ -\frac{1}{2}& \frac{\sqrt{3}}{2}& 2\\ -\frac{1}{2}& -\frac{\sqrt{3}}{2}& 1\end{array}\right]$

Under three-phase alternating current busbar voltage static coordinate, vector representation is:

v _αβ0＝[v _α(t)v _β(t)v ₀(t)] ^T

Can obtain vector under ac bus voltage static coordinate by Clarke conversion is

v _αβ0＝Cv _abc＝[V _msin(β)-V _mcos(β)0] ^Tv _abc＝C ^-1v _αβ0

Three-phase alternating current busbar voltage V _abc(t) as input voltage signal, obtain the phase value θ of input voltage signal through phase-locked loop, pass through again feedback element sin (θ) and the cos (θ) of phase-locked loop, obtain feedback signal Vsin (θ) and the Vcos (θ) of these two trigonometric functions, Vsin (θ) and input signal v _α(t) product, Vcos (θ) and input signal v _β(t) product, the sum of products is as the input signal of proportional integral link, the input signal v of ratio-integral element _pIfor:

$v_{\mathrm{PI}}=[V_m\sin \left(\mathrm{\β}\right)-V_m\cos \left(\mathrm{\β}\right)]\left[\begin{array}{c}{V}_m^{-1}\cos \left(\mathrm{\θ}\right)\\ V_m^{-1}\sin \left(\mathrm{\θ}\right)\end{array}\right]=\sin \left(\mathrm{\β}\right)\cos \left(\mathrm{\θ}\right)-\cos \left(\mathrm{\β}\right)\sin \left(\mathrm{\θ}\right)$

Phase-locked loop can accurately be followed the tracks of the phase value of input voltage signal, and the phase value that three-phase positive sequence voltage signal obtains input voltage through phase-locked loop is θ=π+β, and the input signal of ratio-integral element is 0;

The transfer function of ratio-integral element is: wherein GP is proportionality coefficient, and GI is integral coefficient, and s Laplacian obtains phase error signal Ph by following formula _err:

${\mathrm{Ph}}_{\mathrm{err}}=(\mathrm{GP}+\frac{\mathrm{GI}}{s})v_{\mathrm{PI}}+2\mathrm{\π}{f}_0$

Phase error signal Ph _errpass through again integral element obtain the phase value of input voltage signal

Wherein, described filtering link comprises low-pass filtering, high-pass filtering and bandpass filtering successively, and described low-pass filtering adopts low pass filter, and described high-pass filtering adopts high pass filter, and described bandpass filtering adopts band pass filter.

The concrete steps of described filtering link are as follows:

Through the phase error signal Ph of digital phase-locked loop link output _errin include supersynchronous frequency-doubled signal, high-frequency harmonic signal, low frequency oscillations signal and the subsynchronous frequency signal of generator unit shaft system mode, in order finally to isolate generator set torsional vibration mode signal, first by phase error signal Ph _errthrough as shown in the formula low pass link, filter out supersynchronous frequency-doubled signal and high-frequency harmonic signal,

$\frac{G_1}{1+2{\mathrm{\ξ}}_1\left(\frac{s}{{\mathrm{\ω}}_{c1}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c1}}\right)}^2}$

Wherein, G ₁for proportionality coefficient, ω _c1for low pass link corner frequency, ξ ₁for damping ratio, s Laplacian;

Secondly through as shown in the formula high pass link, filter out low frequency oscillations signal,

$\frac{G_2{\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)}^2}{1+2{\mathrm{\ξ}}_2\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)}^2}$

Wherein, G ₂for proportionality coefficient, ω _c2for high pass link corner frequency, ξ ₂for damping ratio, s Laplacian;

Again through as shown in the formula the logical link of band, isolate the subsynchronous frequency signal of generator unit shaft system mode of appointment,

$\frac{G_3\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)}{1+2{\mathrm{\ξ}}_3\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)}^2}$

Wherein G ₃for proportionality coefficient, ω _c3for being with logical link corner frequency, ξ ₃for damping ratio, s Laplacian;

Pass through the subsynchronous frequency signal that above-mentioned filtering link obtains, can reflect the torsional oscillation amplification level of the nearer generator set torsional vibration mode signal of electrical distance, the component of voltage frequency that is reflected in the subsynchronous frequency signal of grid side is f _d=50-f _shertz, wherein f _dfor the component of voltage frequency of subsynchronous frequency signal, f _sfor the frequency of generator set torsional vibration mode signal, [the 50-f containing in phase error signal _d]=[50-(50-f _s)]=f _shertz, the generator set torsional vibration mode signal that obtained exactly.

The invention has the beneficial effects as follows:

For the stability limit that improves circuit increases ability to transmit electricity; Thermal Power Bases generally adopts series compensation technology of transmission of electricity or high voltage dc transmission technology Transmission Mode; may cause that many fired power generating unit of sending end face sub-synchronous oscillation problem, need to adopt multiple inhibition and safeguard measure combination to solve the sub-synchronous oscillation problem of Thermal Power Bases.Sub-synchronous oscillation suppresses and protective device can be installed near the distolateral installation of machine and grid side; shaft system of unit tach signal is that the distolateral sub-synchronous oscillation of reliable machine suppresses and protective device control inputs signal; if and the inhibition of grid side sub-synchronous oscillation and protective device are taked to same method; the multiple units of Thermal Power Bases need to be by longer communication channel access signal; project cost is higher, coordinates to control complexity and may reduce reliability.The present invention proposes to adopt sub-synchronous oscillation to suppress and the bus alternating voltage of protective device access point is source signal; obtain shaft system of unit torsional oscillation mode signal by digital phase-locked loop and digital processing technology; cost is lower and be easy to realization, can be on the spot for device provides reliable control inputs signal.

Brief description of the drawings

Fig. 1 is thermoelectric generator group axle system and tachometric survey schematic diagram in prior art;

Fig. 2 is the structural representation of digital phase-locked loop (PLO), and in figure, PI is ratio-integral element, and GP is proportionality coefficient, and GI is integral coefficient, ω _ofor power frequency synchronous angular velocity;

Fig. 3 is phase error signal is isolated torsional oscillation mode signal view by filtering link;

Fig. 4 is that generator shaft is rotating speed and synchronous speed aberration curve figure;

Fig. 5 is bus three-phase alternating voltage oscillogram;

Fig. 6 is digital phase-locked loop output voltage phase waveform figure;

Fig. 7 is phase error signal oscillogram in digital phase-locked loop;

Fig. 8 is the spectrum analysis figure of phase error signal in digital phase-locked loop;

Fig. 9 is that existing axle is that tach signal mode is mode curve comparison diagram with adopting digital phase-locked loop to measure axle;

Figure 10 is that existing axle is that tach signal mode is the local curve comparison diagram of mode with adopting digital phase-locked loop to measure axle;

Embodiment

Below in conjunction with accompanying drawing, the acquisition methods of sub-synchronous oscillation inhibition of the present invention and protective device control inputs signal is further described in detail.

The acquisition methods of sub-synchronous oscillation inhibition of the present invention and protective device control inputs signal, with the three-phase alternating current busbar voltage V of sub-synchronous oscillation inhibition and protective device access point _abc(t), as input voltage signal, this input voltage signal is transformed to the orthogonal static coordinate signal of two-phase V through Clarke _α, V _β, the orthogonal static coordinate signal of two-phase V _αand V (t) _β(t) through digital phase-locked loop link output phase error signal Ph _err; Phase error signal Ph _errlink is isolated the control inputs signal of generator set torsional vibration mode signal as sub-synchronous oscillation inhibition and protective device after filtering.Digital phase-locked loop link comprises ratio-integral element, integral element and feedback element; Filtering link comprises low-pass filtering, high-pass filtering and bandpass filtering, and low-pass filtering adopts low pass filter, and high-pass filtering adopts high pass filter, and bandpass filtering adopts band pass filter.

Phase-locked loop is common component in control system, adopts feedback principle, in the time that the frequency of pll output signal and the frequency of input signal equate, and the fixing difference of phase preserving of two signals.Be illustrated in figure 2 digital phase-locked loop (PLO) structural representation, in high voltage dc transmission technology (HVDC) and Survey of Flexible AC Transmission System Technology (FACTs), as power-frequency voltage synchronism link, input signal is ac bus three-phase voltage V _abc(t), be transformed to the orthogonal static coordinate signal of two-phase V through Clark _{α β}(t), through ratio-integral element (PI link) and feedback element regulating action, output AC voltage signal V _a(t) phase value θ.

Due to three-phase alternating current busbar voltage V _abc(t) in, containing time frequency component of voltage is:

$\left\{\begin{array}{c}{\mathrm{\Δv}}_{\mathrm{sa}}\left(t\right)=V_s\cos \left(2\mathrm{\π}{f}_{d}t\right)\\ {\mathrm{\Δv}}_{\mathrm{sb}}\left(t\right)=V_s\cos (2\mathrm{\π}{f}_{d}t-2/3\mathrm{\π})\\ {\mathrm{\Δv}}_{\mathrm{sc}}\left(t\right)=V_s\cos (2\mathrm{\π}{f}_{d}t+2/3\mathrm{\π})\end{array}\right.---\left(1\right)$

$\left\{\begin{array}{c}{\mathrm{\Δv}}_{\mathrm{sa}}\left(t\right)=V_s\cos \left(2\mathrm{\π}{f}_{d}t\right)\\ {\mathrm{\Δv}}_{\mathrm{sb}}\left(t\right)=V_s\cos (2\mathrm{\π}{f}_{d}t-2/3\mathrm{\π})\\ {\mathrm{\Δv}}_{\mathrm{sc}}\left(t\right)=V_s\cos (2\mathrm{\π}{f}_{d}t+2/3\mathrm{\π})\end{array}\right.---\left(2\right)$

F in formula _dfor inferior frequency electric voltage frequency, so the phase error signal Ph of digital phase-locked loop link output _errin contain with busbar voltage in the frequency signal of the frequency complementary of voltage time frequently.If time frequency component of voltage " positive sequence is to weighing " form, phase error signal Ph as shown in above formula (1) in three-phase bus voltage _errin contain frequency for (f ₀-f _d) and 2 (f ₀-f _d) signal component, wherein f ₀for synchronized electric voltage frequency; If time frequency component of voltage " negative phase-sequence is to weighing " form, phase error signal Ph as shown in above formula (2) in three-phase alternating voltage _errin contain frequency for (f ₀+ f _d) and 2 (f ₀+ f _d) signal component, the ratio that supersynchronous harmonic accounts for is less;

Because system disturbance produces " symmetry " inferior frequency voltage/current component at Generator end, because the elements such as the circuit of real system are asymmetric and HVDC or FACTs electronic power switch action non-linear process, in ac bus voltage, time frequency voltage may contain " asymmetric " component, thereby contains (f in power frequency synchronism link phase-locked loop _s± f _d) and 2 (f _s± f _d) frequency series of signals.Dimension frequency component of voltage exists and causes that power frequency is asymmetric in addition, forms negative phase-sequence (100Hz) component, and subsynchronous frequency signal component proportion is greater than other components.

Suppose that unit shafting torsional oscillation mode frequency is f _shertz, being reflected in the subsynchronous component of voltage frequency of grid side is f _d=50-f _shertz, through phase-locked loop link, wherein in error phase signal, will contain [50-f _d]=[50-(50-f _s)]=f _shertz, obtained exactly shaft system of unit torsional oscillation mode signal.

Time frequency component of voltage frequency sum in the subsynchronous oscillation model frequency of shaft system of unit and electrical network is synchronized frequency, the phase error signal Ph of digital phase-locked loop _errin be also synchronized frequency lower than time frequently component of voltage frequency sum in the signal component frequency of synchronizing frequency and electrical network, thereby Ph _errin subsynchronous signal frequency equate with the subsynchronous oscillation model frequency of shaft system of unit, this signal is the same with shaft system of unit tach signal can reflect the torsional oscillation level of axle system.As shown in Figure 4, Ph _errsignal obtains generator set torsional vibration mode signal after filtering, can also carry out mode decomposition to mode signal as required.Can be used as with unit and have the sub-synchronous oscillation inhibition of certain distance and the control inputs signal of protective device.

Embodiment

With many, base of certain coal electricity large electric power plant unit by remote high-power the transmitting electric power as example of high voltage direct current transmission project, show through research, coal electricity base is in islanded system mode, after boosting, grid-connected unit is directly connected with high voltage direct current transmission converting plant ac bus, electrical couplings is tight, start shooting when less sub-synchronous oscillation problem occurs, i.e. shaft system of unit low order torsional oscillation mode generation amplification phenomenon of torsional vibration, may cause axle system tired or damage.Need to take sub-synchronous oscillation braking measure to solve shaft system of unit torsional oscillation instability problem.

Sub-synchronous oscillation suppresses and protective device needs can characterize sub-synchronous oscillation characteristic signals as input control signal, measures shaft system of unit real-time rotate speed as shown in Figure 1 by speed probe, has directly reflected as shown in Figure 4 shafting torsional oscillation characteristic.When the input control signal of net lateral inhibition and protective device adopts the method, the axle of multiple units is that tach signal all needs by certain distance traffic channel to device, and engineering cost, compared with high and intermediate link is many, reduces the reliability of engineering.

For example coal electricity base unit and converting plant connected system mode, shaft system of unit is 4 mass models, wherein low order torsional oscillation mode frequency is 12.72Hz.Adopt converting plant three-phase bus alternating voltage V as shown in Figure 5 _abc(t), as input signal, as shown in Figure 2, this input signal is transformed to the orthogonal static coordinate signal of two-phase V through Clarke _αand V (t) _β(t), V _αand V (t) _β(t) with the feedback signal sum of products, through proportional plus integral control link (GP=2000.0, GI=1.0), output AC voltage signal V _a(t) as shown in Figure 6, described phase value θ forms feedback signal through trigonometric function link to phase value θ, composition digital phase-locked loop closed loop controlling structure.

As shown in Figure 7, the proportional plus integral control link output phase error signal Ph of digital phase-locked loop _err, signal spectral analysis as shown in Figure 8.This signal is through low pass link (G ₁=1.0, ω _c1=219.9, ξ ₁=0.5) conversion, then pass through high pass link (G ₂=1.0, ω _c2=62.8, ξ ₂=0.5) conversion, known shaft system of unit low order torsional oscillation mode frequency is 12.72Hz, high pass link is processed rear signal through the logical link (G of band ₃=12.0, ω _c3=79.9, ξ ₃=0.15) conversion, isolates shaft system of unit single order mode (12.72Hz) torsional vibration signals.If Fig. 9 and Figure 10 are model analysis and bus three-phase alternating voltage mode analysis waveform comparison diagram after phase-locked loop is measured after existing direct measurement shaft system of unit rotating speed.As seen from the figure; bus three-phase alternating voltage is through phase-locked loop link; wherein to have comprised fired power generating unit axle be mode torsional oscillation level to phase error signal; again after filtering signal after processing, to obtain mode signal consistent with model analysis after direct measurement shaft system of unit rotating speed, can be used as the control inputs signal of subsynchronous restraining device and protective device.

Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit, although the present invention is had been described in detail with reference to above-described embodiment, those of ordinary skill in the field are to be understood that: still can modify or be equal to replacement the specific embodiment of the present invention, and do not depart from any amendment of spirit and scope of the invention or be equal to replacement, it all should be encompassed in the middle of claim scope of the present invention.

Claims (3)

1. an acquisition methods for sub-synchronous oscillation inhibition and protective device control inputs signal, is characterized in that: the method is with the three-phase alternating current busbar voltage V of sub-synchronous oscillation inhibition and protective device access point _abc(t), as input voltage signal, this input voltage signal is transformed to the orthogonal static coordinate signal of two-phase V through Clarke _α(t), V _β(t), the orthogonal static coordinate signal of two-phase V _αand V (t) _β(t) through digital phase-locked loop link output phase error signal Ph _err; Phase error signal Ph _errlink is isolated the control inputs signal of generator set torsional vibration mode signal as sub-synchronous oscillation inhibition and protective device after filtering;

Described digital phase-locked loop link comprises ratio-integral element, integral element and feedback element, and its concrete steps are as follows:

If synchronized frequency is f ₀=50Hz, synchronous phase angle is β=ω ₀t=2 π f ₀t, three-phase alternating current busbar voltage is:

$\left\{\begin{array}{c}{v}_a=V_m\sin \left(\mathrm{\β}\right)\\ v_b=V_m\sin (\mathrm{\β}-\frac{2\mathrm{\π}}{3})\\ v_c=V_m\sin (\mathrm{\β}+\frac{2\mathrm{\π}}{3})\end{array}\right.$

Represent by vector form: v _abc=[v _av _bv _c] ^t

C is Clarke Clarke transformation matrix, C ^-1for inverse-transform matrix:

$C=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\\ \frac{1}{2}& \frac{1}{2}& \frac{1}{2}\end{array}\right],$ $C^{-1}=\left[\begin{array}{ccc}1& -\frac{1}{2}& 1\\ -\frac{1}{2}& \frac{\sqrt{3}}{2}& 1\\ -\frac{1}{2}& -\frac{\sqrt{3}}{2}& 1\end{array}\right]$

Under three-phase alternating current busbar voltage static coordinate, vector representation is:

v _αβ0＝[v _α(t)?v _β(t)?v ₀(t)] ^T

Obtaining vector under ac bus voltage static coordinate by Clarke conversion is

v _αβ0＝Cv _abc＝[V _msin(β)?-V _mcos(β)?0] ^T?v _abc＝C ^-1v _αβ0

Three-phase alternating current busbar voltage V _abc(t) as input voltage signal, obtain the phase value θ of input voltage signal through phase-locked loop, pass through again feedback element sin (θ) and the cos (θ) of phase-locked loop, obtain feedback signal Vsin (θ) and the Vcos (θ) of these two trigonometric functions, Vsin (θ) and input signal v _α(t) product, Vcos (θ) and input signal v _β(t) product, the sum of products is as the input signal of ratio-integral element, the input signal v of ratio-integral element _pIfor:

$v_{\mathrm{PI}}=[V_m\sin \left(\mathrm{\β}\right)-V_m\cos \left(\mathrm{\β}\right)]\left[\begin{array}{c}{V}_m^{-1}\cos \left(\mathrm{\θ}\right)\\ V_m^{-1}\sin \left(\mathrm{\θ}\right)\end{array}\right]=\sin \left(\mathrm{\β}\right)\cos \left(\mathrm{\θ}\right)-\cos \left(\mathrm{\β}\right)\sin \left(\mathrm{\θ}\right)$

Phase-locked loop can accurately be followed the tracks of the phase value of input voltage signal, and the phase value that three-phase positive sequence voltage signal obtains input voltage through phase-locked loop is θ=π+β, and the input signal of ratio-integral element is 0;

The transfer function of ratio-integral element is: wherein GP is proportionality coefficient, and GI is integral coefficient, and s Laplacian obtains phase error signal Ph by following formula _err:

${\mathrm{Ph}}_{\mathrm{err}}=(\mathrm{GP}+\frac{\mathrm{GI}}{s})v_{\mathrm{PI}}+2\mathrm{\π}{f}_0$

Phase error signal Ph _errpass through again integral element obtain the phase value of input voltage signal

2. the acquisition methods of sub-synchronous oscillation inhibition as claimed in claim 1 and protective device control inputs signal; it is characterized in that: described filtering link comprises low-pass filtering, high-pass filtering and bandpass filtering successively; described low-pass filtering adopts low pass filter; described high-pass filtering adopts high pass filter, and described bandpass filtering adopts band pass filter.

3. the acquisition methods of sub-synchronous oscillation inhibition as claimed in claim 2 and protective device control inputs signal, is characterized in that: the concrete steps of described filtering link are as follows:

Through the phase error signal Ph of digital phase-locked loop link output _errin include supersynchronous frequency-doubled signal, high-frequency harmonic signal, low frequency oscillations signal and the subsynchronous frequency signal of generator unit shaft system mode, in order finally to isolate generator set torsional vibration mode signal, first by phase error signal Ph _errthrough as shown in the formula low pass link, filter out supersynchronous frequency-doubled signal and high-frequency harmonic signal,

$\frac{G_1}{1+2{\mathrm{\ξ}}_1\left(\frac{s}{{\mathrm{\ω}}_{c1}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c1}}\right)}^2}$

Wherein, G ₁for proportionality coefficient, ω _c1for low pass link corner frequency, ξ ₁for damping ratio, s Laplacian;

Secondly through as shown in the formula high pass link, filter out low frequency oscillations signal,

$\frac{G_2{\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)}^2}{1+2{\mathrm{\ξ}}_2\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c2}}\right)}^2}$

Wherein, G ₂for proportionality coefficient, ω _c2for high pass link corner frequency, ξ ₂for damping ratio, s Laplacian;

Again through as shown in the formula the logical link of band, isolate the subsynchronous frequency signal of generator unit shaft system mode of appointment,

$\frac{G_3\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)}{1+2{\mathrm{\ξ}}_3\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)+{\left(\frac{s}{{\mathrm{\ω}}_{c3}}\right)}^2}$

Wherein G ₃for proportionality coefficient, ω _c3for being with logical link corner frequency, ξ ₃for damping ratio, s Laplacian;

Pass through the subsynchronous frequency signal that above-mentioned filtering link obtains, can reflect the torsional oscillation amplification level of the nearer generator set torsional vibration mode signal of electrical distance, the component of voltage frequency that is reflected in the subsynchronous frequency signal of grid side is f _d=50-f _shertz, wherein f _dfor the component of voltage frequency of subsynchronous frequency signal, f _sfor the frequency of generator set torsional vibration mode signal, [the 50-f containing in phase error signal _d]=[50-(50-f _s)]=f _shertz, the generator set torsional vibration mode signal that obtained exactly.