Low-frequency band suppression enhanced anti-reversal power system stabilizer

Abstract

A low-frequency band suppression enhanced anti-reversal power system stabilizer is presented by the invention. Currently the widely used PSS2B power system stabilizer needs lead elements above Order 2 to meet the phase compensation requirement of DC blocking signal of active power, thus quickly increasing high-frequency band gain, restricting allowable total setting gain of PSS, limiting low-band gain and reducing low-frequency band suppression ability of power system stabilizer. The invention will add generator speed signal (which is treated by DC blocking element and corrected by parallel proportional differential PD) and active power signal P.sub.e (which is treated by DC blocking element and gained by gain factor K.sub.s3) to get equivalent synthetic mechanical power of power system stabilizer. The actual active power signal gained by gain factor K.sub.S1 can meet the requirement of phase compensation through Order 1 lead and lag elements, thus increasing allowable total setting gain of PSS and improving the ability of low-frequency band oscillation suppression.

Claims

1. A method of suppressing low frequency active power oscillation with minimum reactive power variation for super-large power grids comprising the steps of: step 1: check generator speed signal , use two-order DC blocking element to get speed fluctuation signal, which is corrected by parallel proportional differential PD to get corrected speed fluctuation signal; step 2: check active power signal of generator P.sub.e, and use 1st order or 2nd order DC blocking element to get fluctuation signal of active power, which is gained by gain factor K.sub.s3 to get gained fluctuation signal of active power; step 3: the gained fluctuation signal of active power in the step 2 is added with the corrected speed fluctuation signal in the step 1 together to become an equivalent synthetic mechanical power for equaling stationary mechanical power from prime mover; step 4: use notching filter to conduct lowpass filtering for the equivalent synthetic mechanical power gotten in the step 3 to get a lowpass filtered signal; step 5: subtract the fluctuation signal of active power in the step 2 from the lowpass filtered signal in the step 4 to get an actual fluctuation signal of active power; step 6: the actual fluctuation signal of active power in the step 5 is gained by gain factor K.sub.s1, then is amended by 1st order lead or lag phase correction respectively and then is limited by upper limit and lower limit to get a final voltage signal suppressing fluctuation signal of active power, which is input to the super-large power grids by a power system stabilizer.

2. The method according to claims 1, wherein a formula of the speed fluctuation signal in the step 1 is $\frac{s T_{w 1}}{1 + s T_{w 1}} \frac{s T_{w 2}}{1 + s T_{w 2}},$ in which T.sub.w1, T.sub.w2 and s mean 1st order DC blocking time constant of speed signal, 2.sup.nd order DC blocking time constant of speed signal and differential operator respectively; a formula of the parallel proportional differential PD correction is
K.sub.w(1+sT.sub.7), in which K.sub.w, T.sub.7 and s mean total proportional amplification factor of correction element, differentiating time constant and differential operator respectively.

3. The method according to claims 2, wherein when obtaining the fluctuation signal of active power in the step 2, a formula is $P_{e} \frac{s T_{w 3}}{1 + s T_{w 3}} \frac{s T_{w 4}}{1 + s T_{w 4}},$ in which T.sub.w3, T.sub.w4 and s mean 1st order DC blocking time constant of active power, 2nd order DC blocking time constant of active power and differential operator respectively.

4. The method according to claims 3, wherein a formula of the equivalent synthetic mechanical power in the step 3 is $\frac{s T_{w 1}}{1 + s T_{w 1}} \frac{s T_{w 2}}{1 + s T_{w 2}} (1 + s T_{7}) K_{w} + P_{e} \frac{s T_{w 3}}{1 + s T_{w 3}} \frac{s T_{w 4}}{1 + s T_{w 4}} K_{s 3},$ in which K.sub.s3 means gain factor of active power.

5. The method according to claims 2, wherein when using the 1st order DC blocking element to obtain fluctuation signal of active power in the step 2, a formula is $P_{e} \frac{s T_{w 3}}{1 + s T_{w 3}},$ in which T.sub.w3 and s mean 1st order blocking time constant of active power and differential operator respectively; a formula of the equivalent synthetic mechanical power is $\frac{s T_{w 1}}{1 + s T_{w 1}} \frac{s T_{w 2}}{1 + s T_{w 2}} (1 + s T_{7}) K_{w} + P_{e} \frac{s T_{w 3}}{1 + s T_{w 3}} K_{s 3},$ in which K.sub.s3 means gain factor of active power.

6. The method according to claims 1, wherein after the 1st order lead or lag phase correction element for actual fluctuation signal of active power in the step 6, conduct 2nd order and 3rd order lead or lag compensation element correction if necessary.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is the model structure of current PSS2B.

(2) FIG. 2 is the phase relation between phase compensation and input signal of current PSS2B. V.sub.pss low, V.sub.pss high, M.sub.pss high and M.sub.pss low mean output in low frequency band, output in high frequency band, moment in high frequency band and moment in low frequency band of PSS2B respectively.

(3) FIG. 3 is the model structure of power system stabilizer (PSS-NEW-B) of this invention.

(4) FIG. 4 is the phase relation between phase compensation and input signal of power system stabilizer (PSS-NEW-B). V.sub.pss low, V.sub.pss high, M.sub.pss high, M.sub.pss low and Vout2 mean output in low frequency band, output in high frequency band, moment in high frequency band, moment in low frequency band and actual fluctuation signal of active power of PSS2B obtained by Step 5 of the invention respectively.

(5) FIG. 5 is the waveform of simulation result of critical amplification factor for current PSS2B and PSS-NEW-B.

(6) FIG. 6 is about 1% load voltage step response of generator when field measured PSS2B is in and out of service.

(7) FIG. 7 is the simulation result of 1% load voltage step demand of generator for different situations when PSS is in and out of services.

(8) FIG. 8 is cutting-off response simulation of three-phase short circuit 0.1 s line at near-end of outlet of power station for different situations when PSS is in and out of services.

DETAIL DESCRIPTION OF THE INVENTION

(9) The invention is further illustrated in combination with all drawings of the instruction.

(10) The structure of power system stabilizer (PSS-NEW-B) model is shown in FIG. 3. Its working steps are as follows:

(11) Step 1: Check generator speed single . Use two-order DC blocking link to get speed fluctuation signal and then correct it by parallel proportional differential PD.

(12) Step 2: Check active power signal of generator P.sub.e, and use Order 2 DC blocking link to get fluctuation signal of active power.

(13) Step 3: After gain by gain factor K.sub.s3, the fluctuation signal of active power in Step 2 by is added with speed fluctuation signal corrected by PD in Step 1 together to become equivalent synthetic mechanical power.

(14) Step 4: Use notching filter to conduct lowpass filtering for equivalent synthetic mechanical power received in Step 3.

(15) Step 5: Subtract fluctuation signal of active power in Step 2 from signal in Step 4 (by lowpass filtering in notching filter) to get actual fluctuation signal of active power.

(16) Step 6: After gained by gain factor K.sub.s1, the actual fluctuation signal of active power in Step 5 is taken as output of power system stabilizer after lead and lag correction by Order 1 respectively and upper & lower amplitude limiting. As backup means for phase correction in special circumstances, Order 3 lead-lag correction is set as lead or lag compensation according to specific situations when relevant requirements cannot be met after Order 2 compensation.

(17) Shown as the phase relation in FIG. 4, when Vout 2 is close to the phase P, PSS-NEW-B typically uses lag compensation in low band and lead compensation in high band. The high-band phase of self-shunt excited or high initial excitation systems is relatively leading, or even needs no extra lead compensation provided by PSS-NEW-B, so the problem of one-way increase of high-band gain is solved.

(18) Further illustrate this invention by taking a 1000 MW steam turbine generator unit as example and considering PSS2B power system stabilizer currently used by the unit as comparison objective.

(19) This unit is of self-shunt excited, and main nominal parameters of generator are as follows:

(20) Rated apparent power: 1120 MVA

(21) Rated active power: 1008 MW

(22) Rated terminal voltage: 27 kV

(23) Rated exciting current: 5041 A

(24) Direct-axis synchronous reactance (unsaturated value): 193.41%

(25) Quadrature axis synchronous reactance (unsaturated value): 193.41%

(26) Direct-axis open circuit time constant: 10.8 s

(27) Adjustment setting of excitation system: 8%

(28) 1. Field Test of Uncompensated Lag Characteristic and Compensation & Setting of Phase Parameters of Generator Excitation System

(29) The unit during field test has active power, reactive power and terminal voltage of 888 MW, 101 MVar and 26.2 kV respectively. The field set PSS2B parameters are shown in Table 1.

(30) TABLE-US-00001 TABLE 1 Setting Parameters of PSS2B Power System Stabilizer Constant Constant Constant Parameter value Parameter value Parameter value T.sub.W1 5 T.sub.8 0.2 T.sub.3 0.22 T.sub.W2 5 T.sub.9 0.1 T.sub.4 0.02 T.sub.W3 5 K.sub.S1 8 T.sub.11 1 T.sub.W4 0 N 1 T.sub.12 1 K.sub.S2 0.6 M 5 V.sub.STMAX 0.05 T.sub.7 5 T.sub.1 0.2 V.sub.STMIN 0.05 K.sub.S3 1 T.sub.2 0.03 V.sub.SI2MAX 1 V.sub.SI1MAX 1 V.sub.SI1MIN 1 V.sub.SI2MIN 1

(31) The parameters of PSS-NEW-B set according to field measured uncompensated lag characteristic of generator excitation system is shown in Table 3.

(32) TABLE-US-00002 TABLE 2 Setting Parameters of PSS-NEW-B Power System Stabilizer Constant Constant Constant Parameter value Parameter value Parameter value T.sub.W1 5 T.sub.8 0.2 T.sub.3 0.23 T.sub.W2 5 T.sub.9 0.1 T.sub.4 0.1 T.sub.W3 5 K.sub.S1 7 T.sub.11 1 T.sub.W4 0 N 1 T.sub.12 1 K.sub.W 1.67 M 5 U.sub.STMAX 0.1 T.sub.7 5 T.sub.1 0.3 U.sub.STMIN 0.1 K.sub.S3 1 T.sub.2 3 V.sub.SI2MAX 1 V.sub.SI1MAX 1 V.sub.SI1MIN 1 V.sub.SI2MIN 1

(33) The phase compensation characteristic according to field measured uncompensated lag characteristic of generator excitation system as well as setting parameters of PSS2B and PSS-NEW-B power system stabilizers are shown in Table 3.

(34) TABLE-US-00003 TABLE 3 Phase Compensation Results of PSS2B and PSS-NEW-B PSS2B PSS-NEW-B Un- PSS2B PSS-NEW-B after- after- compen- compen- compen- compen- compen- Fre- sated sation sation sation sation quen- lag angle angle angle angle angle cy(Hz) () () () () () 0.08 34.90 35.90 23.07 70.80 57.97 0.16 44.55 47.67 37.55 92.22 82.10 0.23 53.16 46.14 37.24 99.29 90.40 0.47 72.41 30.65 23.86 103.06 96.27 0.63 77.19 20.96 16.26 98.15 93.45 0.86 83.66 10.23 9.44 93.90 93.10 1.02 93.54 5.39 6.87 98.93 100.41 1.25 104.98 0.78 5.19 105.77 110.17 1.41 115.49 0.93 4.94 114.55 120.43 1.56 123.01 1.83 5.14 121.18 128.15 1.80 106.26 2.02 6.05 104.24 112.31 2.03 108.75 1.18 7.32 107.57 116.07

(35) Table 3 shows that in setting parameters and with the range of 0.2 Hz2.0 Hz, the compensated lag characteristic angles of PSS2B and PSS-NEW-B are within specified 80135, and they are within specified 4590. The phase compensation result meets the requirements of relevant standards.

(36) 2. Setting of Total Amplification Factor K.sub.s1 of Power System Stabilizer

(37) Use Order 6 model of above generator built on PSASP program platform. Apply custom function of model to build measured excitation system, parameters and various PSS models for simulation computation and analysis. Adjust the working conditions of unit to make it accord with those during field setting field. Gradually increase gain K.sub.S1 of PSS2B and PSS-NEW-B respectively till diverging oscillation emerges in exciting voltage of generator. By this time, the K.sub.S1 set value means respective critical amplification factor of two types of PSS. The critical amplification factor of PSS2B and PSS-NEW-B is 87 and 72 referring to simulation result in FIG. 5.

(38) The field set amplification factor of PSS2B is 8. According to the principle of rounding of 1/10 critical amplification factor, the amplification factor of PSS-NEW-B is 7.

(39) 3. Comparison of Measurement and Simulation of Load Step Response

(40) The working conditions of above 1000 MW unit are P=888 MW, Q=101 MVar, Ug=26.2 kV and Xc=8%. FIG. 6 shows field measured 1% load voltage step response of generator when PSS2B power system stabilizer is in and out of service.

(41) Use PSASP simulation platform to simulate 1% load step demand of generator when PSS, PSS2B and PSS-NEW-B are not in service. See FIG. 7 for the results.

(42) Table 4 shows oscillation quality parameters of measured and simulated active power.

(43) TABLE-US-00004 TABLE 4 Oscillation Quality Parameters of Measured and Simulated 1% Load Voltage Step Response of Generator In and out of Oscillation Damping Items service of PSS Frequency (Hz) Ratio D Measurement PSS is out of service. 1.42 0.08 PSS2B is in service. 1.44 0.29 Simulation PSS is out of service. 1.42 0.09 PSS2B is in service. 1.38 0.28 PSS-NEW-B is in service. 1.38 >>0.5

(44) Table 4 shows that the simulated and measured results are the same when PSS2B is in and out of service, proving that the simulation result is authentic. Judging from load voltage step response waveform and response quality parameters calculated accordingly, the oscillation of active power quiets down quickly after PSS-NEW-B is in service, and additional damping provided is far bigger than that of PSS2B, showing that PSS-NEW-B has better ability in low-band oscillation suppression than PSS2B.

(45) 4. Simulation Comparison of Recovery Ability after Three-Phase Short Circuit

(46) Use PSASP simulation platform. Set three-phase short circuit fault at near-end of 500 kV outlet of power station. Simulate relay protection action after 0.1 s. Cut off fault lines, and check recovery waveform of active power afterwards. See FIG. 8 for details.

(47) Judging from FIG. 8, the sequence of recovery rate of active power is PSS-NEW-B, PSS2B and PSS out of service. However, if PSS-NEW-B is in service, the oscillation of active power after fault line is cut off quiets down quickly, and the effect of power oscillation suppression is good, showing that PSS-NEW-B power system stabilizer is able to provide better ability in power oscillation suppression than PSS2B, thus good for dynamic stability of power system.

Low-frequency band suppression enhanced anti-reversal power system stabilizer

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H02P9/102

ELECTRICITY

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H02P11/00

ELECTRICITY

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H02H7/06

ELECTRICITY

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H02P9/00

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H02P9/10

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Abstract

Claims

Description