CN104009614A - Static excitation system synchronous signal detection method based on filtering and phase modulating - Google Patents

Abstract

The invention discloses a static excitation system synchronous signal detection method based on filtering and phase modulating. According to the method, by means of a high-voltage modulating transformer and a low-voltage modulating transformer, anode voltage is modulated to be within a range required by a synchronous voltage detection plate; voltage signals are discretized through a digital collecting unit, and a phase commutation notch of the anode voltage is eliminated through band-pass filtering; synchronous signal phase delay brought by filtering introduction is compensated through a differentiation element; through phase modulating of multi-phase voltage, detection of multiple paths of redundant synchronous signals is achieved, zero-crossing detection is carried out on the basis, and a synchronous signal of a thyristor trigger circuit is output. Accordingly, digital detection of the synchronous signal is achieved, the problem that detection precision is low when a simulation circuit is used is avoided, the misjudgment risk existing in zero-crossing detection is avoided, and instantaneity and accuracy of the synchronous signal are guaranteed.

Description

Static excitation system sychronizing signal detecting method based on filtering and phase coordination

Technical field

The invention belongs to electric power system synchronous generator static excitation system technical field, particularly adopting controllable silicon rectifying bridge is the synchronous signal obtaining field of the static excitation system of power rectification device.

Background technology

Excitation system is the important component part of synchronous generator in electric power system, is a kind of automatics that rotor DC excitation electric current is provided to generator.

Excitation system involved in the present invention is being born regulator generator output voltage and idle responsibility, its main circuit adopts three-phase fully-controlled bridge rectification circuit (also claiming rectifier bridge), main element is controllable silicon, and the synchronous voltage signal of its circuits for triggering is provided by the anode voltage of rectification circuit.The accuracy of synchronous voltage signal phase place has determined the accuracy of SCR trigger pulse, directly have influence on the output current of excitation system, and then the output voltage of decision generator unit stator, be also the final output of generator, the visible importance of this synchronizing signal in excitation system that accurately detects.

At present, the sychronizing signal detecting method extensively adopting is zero passage detection method, and the zero crossing of getting synchronizing signal is that benchmark is determined silicon controlled trigger angle.The method can ensure steady operation in the time that generator system normally moves.But, adopt the method to have certain erroneous judgement risk, be embodied in: due to the requirement of system, control signal can be in the time of a phase controllable silicon still conducting, trigger another phase controllable silicon, the controllable silicon of original conducting is turn-offed owing to bearing reverse voltage, and controllable silicon shutoff needs the time, and the rotor that the load of main circuit is generator (being equivalent to a large inductance), inductive current can not suddenly change, the moment of therefore turn-offing at certain phase controllable silicon, the electric current of main circuit can not drop to zero immediately, make in commutation process two-phase in short-circuit condition, cause the anode voltage of rectifier bridge to occur saltus step, form commutation notch, due to the existence of commutation notch, cause the waveform of anode voltage repeatedly through zero point, it is no longer the trigonometric function waveform of standard, will cause like this trigger impulse mistake, the final output voltage that affects excitation system, cause generator output voltage and desired inconsistent.Therefore, invent a kind of erroneous judgement risk of avoiding adopting the existence of zero passage detection method, ensure that the real-time of synchronizing signal and the method for accuracy are extremely urgent.

Summary of the invention

The object of the invention is to improve the defect of original zero passage detection method, avoid the many zero crossings of rectification circuit anode voltage to cause existing while adopting zero passage detection method the problem of trigger impulse mistake, make the synchronizing signal obtaining there is redundancy, by digitized detection, improve the reliability of synchronizing signal simultaneously.

The object of the invention is to realize by following steps:

1) anode voltage of high pressure conditioning transformer (1) access excitation system rectifier bridge (4), the output of high pressure conditioning transformer (1) is connected to the input of low pressure conditioning transformer (2); Low pressure conditioning transformer (2) access synchronization signal detection plate (3);

2) power rectification device and integral link thereof to be detected are numbered: six controllable silicons are numbered respectively to T ₁, T ₂, T ₃, T ₄, T ₅and T ₆, the three-phase alternating current input signal of rectifying device represents with UA, UB, UC respectively;

3) select digital signal processor: determine and the sample frequency of processor ensure f according to parameter computing time of the operating frequency range of power rectification device anode signal, detection synchronizing signal algorithm _s>=5f _uand f _s>=1/T _proc, wherein, f _sfor the sample frequency of digital signal processor, f _ufor the maximum operation frequency of anode signal, T _procfor the computing time of algorithm;

4) model of calculative determination measurement mechanism transformer and parameter: ac input signal UA, UB, the UC of rectifying device are drawn, be connected to respectively the primary side of transformer, utilize the connected mode of transformer and no-load voltage ratio to set, make the voltage signal U that its output amplitude is ± 10V _ab, U _bc, U _ca, transformer output voltage should meet the input range requirement of digital sample plate, and this requirement is determined according to the technical parameter of digital signal processor;

5) by the output voltage signal U of transformer _ab, U _bc, U _cabe connected on three input ports of digital signal processor, by the digital sample function of data acquisition port, process the voltage signal that obtains discretization, be labeled as and there is following relation

${\stackrel{\‾}{U}}_{\mathrm{ab}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{ab}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(1\right)$

${\stackrel{\‾}{U}}_{\mathrm{ca}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{ca}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(2\right)$

${\stackrel{\‾}{U}}_{\mathrm{bc}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{bc}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(3\right)$

Wherein, T _sfor the sampling period of signal, δ (t-nT _s) be sampling function, and meet

$\mathrm{\δ}(t-n{T}_s)=\left\{\begin{array}{cc}1& t=n{T}_s\\ 0& t\≠n{T}_s\end{array}\right.---\left(4\right)$

6) filtering high order harmonic component in three road discrete phase voltage signals: according to the passband width of the operating frequency range select tape bandpass filter of anode voltage signal, filter is selected voltage controlled voltage source second-order bandpass filter, and its transfer function expression formula is

$Y\left(s\right)=X\left(s\right)\frac{\mathrm{sRC}}{1+[3-X\left(s\right)]\mathrm{sRC}+{\left(\mathrm{sRC}\right)}^2}---\left(5\right)$

Wherein, the image function that X (s) is three-phase voltage signal, also, X (s) is the image function of signal after filtering, the centre frequency of filter is according to the centre frequency of filter and free transmission range, determine corresponding filter parameter R and C, the computing formula of upper limiting frequency and lower frequency limit is:

$\left\{\begin{array}{c}{f}_{p1}=\frac{f_0}{2}[\sqrt{{(3-K)}^2+4}-(3-K)]\\ f_{p2}=\frac{f_0}{2}[\sqrt{{(3-K)}^2+4}+(3-K)]\\ K=1+\frac{R_f}{R}\end{array}\right.---\left(6\right)$

Wherein, f _p1for lower frequency limit, f _p2for upper limiting frequency, K is multiplication factor, R _ffor feedback resistance value, R is feedforward resistance value;

7) by the S territory transfer function in step 6, be converted into the transfer function on Z territory

$H\left(z\right)=\frac{\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_k{z}^{-k}}{1-\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{a}_k{z}^{-k}}=\frac{Y\left(z\right)}{X\left(z\right)}---\left(7\right)$

Being expressed as difference equation is

$y\left(n\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{a}_{k}y(n-k)+\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_{x}x(n-k)---\left(8\right)$

Wherein, x (n) is that digital sample plate collects San road discrete phase voltage signal sequence, and y (n) is Hou tri-road discrete phase voltage signal sequences after filtering, a _kand b _kfor corresponding coefficient, the order that N and M are difference equation, the design definite and coefficient of order need to obtain according to different filter design methods;

8) design digital filter: a., by the technical indicator of digital filter, is converted to corresponding analog filter technical indicator; B. according to after conversion technical indicator, design obtains analog bandpass filtering device H (s); C. H (s) is converted to H (z), the signal after digital filtering is designated as

9) incite somebody to action Hou tri-road phase voltage signals after filtering carry out phase compensation: compensation adopts digital differentiation element, and its corresponding analog transfer function is

$G\left(s\right)=\frac{1+a{T}_{c}s}{1+T_{c}s}---\left(9\right)$

Wherein, a and T _cfor parameter to be designed, determine according to phase compensation, transfer function is converted into the transfer function in z territory, obtain

$H\left(z\right)=\frac{\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_k{z}^{-k}}{1-\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{a}_k{z}^{-k}}=\frac{Y_c\left(z\right)}{X_c\left(z\right)}---\left(10\right)$

Further be translated into difference equation, can obtain

$y_c\left(n\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{a}_k{y}_c(n-k)+\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_x{x}_c(n-k)---\left(11\right)$

Wherein, y _c(n) be the output sequence of differentiation element, x _c(n) be the list entries of differentiation element, and compensation Hou tri-road phase voltage signals are designated as with

10) the two-way phase voltage signal after compensation is carried out to phase coordination, realize the input of redundancy, concrete formula is as follows:

Wherein, y _o(n) be the output signal sequence after phase coordination; N[] be fault discriminant function, in the time that the signal of its input exists fault, it is output as 0, otherwise is output as 1, T _d1and T _d2it is respectively signal with with respect to leading phase, T _sfor the sampling time of digital signal processor, T _d1and T _d2should be T _sintegral multiple;

11) to the phase voltage output signal sequence y after coordinating _o(n) carry out zero passage detection, obtain synchronizing signal y _out(n): the expression formula of zero passage detection link is

$y_{\mathrm{out}}\left(n\right)=\left\{\begin{array}{cc}{y}_{\max }& \left|y_o\left(n\right)\right|\≤y_{o\min }\\ 0& \left|y_o\left(n\right)\right|>y_{o\min }\end{array}\right.---\left(13\right)$

Wherein, y _maxoutput while representing signal zero passage, y _ominfor a parameter of setting, work as y _o(n), when absolute value is less than it, just think y _o(n) be less than 0, can have according to circumstances set, suggestion is set to 0 conventionally;

12) gate voltage of control silicon controlled rectifier: the synchronizing signal y obtaining in detection _out(n), on basis, the pilot angle that stack is calculated by excitation system automatic voltage regulator, as the start pulse signal of silicon controlled rectifier, in order to control silicon controlled gate voltage.

Operation principle

The anode voltage of silicon controlled rectifier, by the conversion of transformer, drops in the voltage range of appointment, obtains the signal of telecommunication that can be gathered by digital signal processor; The input port of digital signal processor, the conversion of arriving continuous quantity by analog quantity, collects the anode voltage signal sequence of discretization; This burst, in digital signal processor, through the processing of nonlinear filtering link, phase compensation link and phase coordination link, obtains removing the discrete anode voltage signal sequence of commutation notch impact; Finally, this burst obtains by having the processing of link of zero crossing detection function, detecting the anode voltage synchronous signal sequence that finally needs.Wherein, collection, nonlinear filtering, phase compensation, phase coordination and the zero passage detection of anode voltage letter sequence are all to realize by digital signal processor, and the measurement of anode voltage realizes by transformer.

Technique effect

The difference of the present invention and traditional zero passage detection method is to have introduced filtering and phase coordination, has avoided the synchronization signal detection Problem-Error that in the past adopts merely zero passage detection method to bring.Adopt the present invention to carry out sequence after synchronization signal detection as shown in Figure 3, the frequency that therefrom can see synchronizing signal is 50Hz, filtering the commutation breach of signal, correct reflection the zero passage situation of anode voltage, there is not the phenomenon of erroneous judgement.Can see from above-mentioned implementation process, the present invention is by band pass filter, filtering high order harmonic component, eliminated the commutation notch of anode voltage; Carry out phase compensation by corresponding differentiation element, overcome the synchronizing signal phase delay of bringing owing to introducing filtering; By the phase coordination of Dui San road anode voltage, realize the synchronization signal detection of Liao San road redundancy, improve detection quality and the redundancy of synchronizing signal.Finally, by the detection to synchronizing signal zero crossing, the synchronizing signal of output thyristor gating circuit has avoided adopting merely zero passage detection method easily to cause the wrong problem that detects in the past, reduce the probability of malfunction of excitation system, improved the safety in operation of excitation system.

Brief description of the drawings

Accompanying drawing 1: silicon controlled rectifier synchronization signal detection schematic diagram

Accompanying drawing 2: three-phase controllable silicon rectifier bridge schematic diagram

Accompanying drawing 3: certain generator anode voltage synchronization signal detection result figure

Accompanying drawing 4: the static excitation system sychronizing signal detecting method flow chart based on filtering and phase coordination

Embodiment

Taking the static excitation system of 135MW generator as example, the specific embodiment of the present invention is described.The operating frequency of this generator is 50Hz, between 45Hz～55Hz, changes, and the anode voltage of excitation system is 450V.The power rectification device of its excitation system adopts three-phase controllable silicon rectification circuit, for realizing the detection to its anode voltage, sets up synchronization signal detection circuit as shown in Figure 1, and according to flow process as shown in Figure 4, concrete execution mode is:

1) power rectification device and integral link thereof to be detected are numbered, as shown in Figure 2: six controllable silicons are numbered respectively 1,2,3,4,5 and 6, the three-phase alternating current input signal of rectifying device represents with UA, UB, UC respectively;

2) because the operating frequency of generator changes between 45Hz～55Hz, determine the digital signal processor that adopts TMS320F28335 model, its dominant frequency is 150MHz, as shown in Figure 1, U1 is digital collection unit, and U2 is filter unit, and U3 is phase compensation unit, U4 is phase coordination Duan Yuan, and U5 is zero passage detection unit;

3) anode voltage of considering excitation system is 450V, and digital signal processor gather signal should be amplitude ± 10V, so choose 1# transformer 450/220 (△ ?Y ?11) and 2# transformer 220V/10V (△ ?Y ?1) two-stage transformer.Ac input signal UA, UB, the UC of rectifying device are drawn, be connected to respectively the primary side of 1# transformer, and output is received on 2# transformer, make the voltage signal U that 2# transformer output amplitude is ± 10V _ab, U _bc, U _ca, as shown in Figure 1;

4) by the output voltage signal U of transformer _ab, U _bc, U _ca, be connected on respectively three input ports of digital signal processor, taking 10kHz as the sampling period, by the digital sample function of data acquisition port, process the voltage signal that obtains discretization, from initial time, be labeled as i=1,2,3 ..., obtain the voltage signal sequence of discretization;

5) contact potential series after discretization is carried out to bandpass filtering, obtain filtered three road phase voltage signals because the central task frequency of anode voltage is 50Hz, the mobility scale of frequency is positive and negative 5Hz, and therefore, selection centre frequency is 50Hz, the band pass filter that passband width is 20Hz, passband scope be 40Hz ?60Hz, be convenient to the clutter beyond filtering operating frequency;

6) to filtered three road phase voltage signals sequence is carried out phase compensation, is compensated Hou tri-road phase voltage signals with concrete formula is:

$G\left(s\right)=\frac{1+0.1s}{0+0.02s}---\left(14\right)$

Taking 10kHz as sample frequency, this transfer function is converted into the transfer function in z territory, obtain

$H\left(z\right)=\frac{4.99-4.985z^{-1}}{1-0.995z^{-1}}---\left(15\right)$

Further be translated into difference equation, can obtain

$y_c\left(n\right)=\underset{k=1}{\overset{1}{\mathrm{\Σ}}}{a}_k{y}_c(n-k)+\underset{k=0}{\overset{1}{\mathrm{\Σ}}}{b}_x{x}_c(n-k)---\left(16\right)$

Wherein, a ₁=0.995, b ₀=4.99, b ₁=-4.985;

7) synchronizing signal is coordinated: detect with reliability, judge its whether fault, and corresponding discriminant function carried out to assignment, if certain road signal breaks down, making its corresponding fault discriminant function value is 0, otherwise is 1, according to the fault discriminant function of signal, calculate the output after phase coordination, computing formula is

T _d1and T _d2it is respectively signal with leading phase, T _sfor the sampling time of digital signal processor, in this example, be 0.0001s, T _d1for 0.0002s, T _d2for 0.0004s.

8) to the phase voltage output signal sequence y after coordinating _o(n), carry out zero passage detection, obtain burst after zero passage detection y (1), y (2), y (3) ..., the form of zero passage detection function is:

$y_{\mathrm{out}}\left(n\right)=\left\{\begin{array}{cc}{y}_{\max }& \left|y_o\left(n\right)\right|\≤0\\ 0& \left|y_o\left(n\right)\right|>0\end{array}\right.$

Y _maxfor signal amplitude that can driving power device gate pole, the sequence after zero passage detection as shown in Figure 3;

9), in the basis of signals obtaining in detection, the pilot angle that stack is calculated by excitation system automatic voltage regulator, as the start pulse signal of silicon controlled rectifier, for the gate pole control of silicon controlled rectifier.

Claims (1)

1. the static excitation system sychronizing signal detecting method based on filtering and phase coordination, is characterized in that: the method comprises the steps:

1) anode voltage of high pressure conditioning transformer (1) access excitation system rectifier bridge (4), the output of high pressure conditioning transformer (1) is connected to the input of low pressure conditioning transformer (2); Low pressure conditioning transformer (2) access synchronization signal detection plate (3);

2) power rectification device and integral link thereof to be detected are numbered: six controllable silicons are numbered respectively to T ₁, T ₂, T ₃, T ₄, T ₅and T ₆, the three-phase alternating current input signal of rectifying device represents with UA, UB, UC respectively;

3) select digital signal processor: determine and the sample frequency of processor should ensure f according to parameter computing time of the operating frequency range of power rectification device anode signal, detection synchronizing signal algorithm _s>=5f _uand f _s>=1/T _proc, wherein, f _sfor the sample frequency of digital signal processor, f _ufor the maximum operation frequency of anode signal, T _procfor the computing time of algorithm;

4) model of calculative determination measurement mechanism transformer and parameter: ac input signal UA, UB, the UC of rectifying device are drawn, be connected to respectively the source of transformer, utilize the connected mode of transformer and no-load voltage ratio to set, make the voltage signal U that its output amplitude is ± 10V _ab, U _bc, U _ca, transformer output voltage should meet the input range requirement of digital sample plate, and this requirement is determined according to the technical parameter of digital signal processor;

5) by the output voltage signal U of transformer _ab, U _bc, U _cabe connected on three input ports of digital signal processor, by the digital sample function of data acquisition port, process the voltage signal that obtains discretization, be labeled as and there is following relation

${\stackrel{\‾}{U}}_{\mathrm{ab}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{ab}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(1\right)$

${\stackrel{\‾}{U}}_{\mathrm{ca}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{ca}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(2\right)$

${\stackrel{\‾}{U}}_{\mathrm{bc}}\left(t\right)=\underset{t=0}{\overset{\∞}{\mathrm{\Σ}}}{U}_{\mathrm{bc}}\left(n{T}_s\right)\mathrm{\δ}(t-n{T}_s)---\left(3\right)$

Wherein, T _sfor the sampling period of signal, δ (t-nT _s) be sampling function, and meet

$\mathrm{\δ}(t-n{T}_s)=\left\{\begin{array}{cc}1& t=n{T}_s\\ 0& t\≠n{T}_s\end{array}\right.---\left(4\right)$

6) filtering high order harmonic component in three road discrete phase voltage signals: according to the passband width of the operating frequency range select tape bandpass filter of anode voltage signal, filter is selected voltage controlled voltage source second-order bandpass filter, and its transfer function expression formula is

$Y\left(s\right)=X\left(s\right)\frac{\mathrm{sRC}}{1+[3-X\left(s\right)]\mathrm{sRC}+{\left(\mathrm{sRC}\right)}^2}---\left(5\right)$

Wherein, the image function that X (s) is three-phase voltage signal, is also the image function of X (s) for signal after filtering, and the centre frequency of filter is according to the centre frequency of filter and free transmission range, determine corresponding filter parameter R and C, the computing formula of upper limiting frequency and lower frequency limit is:

$\left\{\begin{array}{c}{f}_{p1}=\frac{f_0}{2}[\sqrt{{(3-K)}^2+4}-(3-K)]\\ f_{p2}=\frac{f_0}{2}[\sqrt{{(3-K)}^2+4}+(3-K)]\\ K=1+\frac{R_f}{R}\end{array}\right.---\left(6\right)$

Wherein, f _p1for lower frequency limit, f _p2for upper limiting frequency, K is multiplication factor, R _ffor feedback resistance value, R is feedforward resistance value;

7) by the S territory transfer function in step 6, be converted into the transfer function on Z territory

$H\left(z\right)=\frac{\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_k{z}^{-k}}{1-\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{a}_k{z}^{-k}}=\frac{Y\left(z\right)}{X\left(z\right)}---\left(7\right)$

Being expressed as difference equation is

$y\left(n\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{a}_{k}y(n-k)+\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_{x}x(n-k)---\left(8\right)$

Wherein, x (n) is that digital sample plate collects San road discrete phase voltage signal sequence, and y (n) is Hou tri-road discrete phase voltage signal sequences after filtering, a _kand b _kfor corresponding coefficient, the order that N and M are difference equation, the design definite and coefficient of order need to obtain according to different filter design methods;

8) design digital filter: a., by the technical indicator of digital filter, is converted to corresponding analog filter technical indicator; B. according to after conversion technical indicator, design obtains analog bandpass filtering device H (s); C. H (s) is converted to H (z), the signal after digital filtering is designated as to U _ab, U _ca, U _bc;

9) to Hou tri-road phase voltage signal U after filtering _ab, U _ca, U _bccarry out phase compensation: compensation adopts digital differentiation element, and its corresponding analog transfer function is

$G\left(s\right)=\frac{1+a{T}_{c}s}{1+T_{c}s}---\left(9\right)$

Wherein, a and T _cfor parameter to be designed, determine according to phase compensation, transfer function is converted into the transfer function in z territory, obtain

$H\left(z\right)=\frac{\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_k{z}^{-k}}{1-\underset{k=1}{\overset{N}{\mathrm{\Σ}}}{a}_k{z}^{-k}}=\frac{Y_c\left(z\right)}{X_c\left(z\right)}---\left(10\right)$

Further be translated into difference equation, can obtain

$y_c\left(n\right)=\underset{k=0}{\overset{N}{\mathrm{\Σ}}}{a}_k{y}_c(n-k)+\underset{k=0}{\overset{M}{\mathrm{\Σ}}}{b}_x{x}_c(n-k)---\left(11\right)$

Wherein, y _c(n) be the output sequence of differentiation element, x _c(n) be the list entries of differentiation element, and compensation Hou tri-road phase voltage signals are designated as with

10) the two-way phase voltage signal after compensation is carried out to phase coordination, realize the input of redundancy, concrete formula is as follows:

Wherein, y _o(n) be the output signal sequence after phase coordination; N[] be fault discriminant function, in the time that the signal of its input exists fault, it is output as 0, otherwise is output as 1, T _d1and T _d2it is respectively signal with with respect to leading phase, T _sfor the sampling time of digital signal processor, T _d1and T _d2should be T _sintegral multiple;

11) to the phase voltage output signal sequence y after coordinating _o(n) carry out zero passage detection, obtain synchronizing signal y _out(n): the expression formula of zero passage detection link is

$y_{\mathrm{out}}\left(n\right)=\left\{\begin{array}{cc}{y}_{\max }& \left|y_o\left(n\right)\right|\≤y_{o\min }\\ 0& \left|y_o\left(n\right)\right|>y_{o\min }\end{array}\right.---\left(13\right)$

Wherein, y _maxoutput while representing signal zero passage, y _ominfor a parameter of setting, work as y _o(n), when absolute value is less than it, just think y _o(n) be less than 0, can have according to circumstances set, suggestion is set to 0 conventionally;

12) gate voltage of control silicon controlled rectifier: the synchronizing signal y obtaining in detection _out(n), on basis, the pilot angle that stack is calculated by excitation system automatic voltage regulator, as the start pulse signal of silicon controlled rectifier, in order to control silicon controlled gate voltage.