Power system stabilizer implementation method for enhancing damping action during power forced oscillation

Abstract

The application discloses a kind of power system stabilizer implementation methods for enhancing power forced oscillation damping effect, by the change of rotating speed and active change quantity are respectively after low-pass filtering and low resistance filtering synthesis obtains rotating speed-power synthesis signal, again after leading-lag correction link, as PSS output.The application generates effective positive damping by the change of rotating speed after filtering when active power forced oscillation occurs in speed regulation system, avoids that the negative damping effect of existing PSS-2B model can intensify active power fluctuation;When machine-network damping oscillation, produce additional positive damping effect similar to in PSS-2B model, and have good anti-adjusting effect.

Description

Technical Field

[0001] This invention relates to a method for implementing power system stabilizers, and more particularly to a method for implementing a power system stabilizer that enhances the damping effect during forced power oscillations. Background Technology

[0002] With the implementation of the State Grid Corporation of China's "Three-North China" (North China, East China, and Central China) UHV AC interconnection and the completion and commissioning of multiple UHV DC lines, a complex, ultra-large synchronous power grid with multiple voltage levels and mixed AC and DC connections has been formed nationwide. The expansion of the AC grid has led to an increase in the equivalent inertia of the entire power system. High-power DC transmission and long-distance heavy-load AC power transmission have reduced the number of generators operating at the receiving end, resulting in significant changes in generator operation methods. This weakens the damping and dynamic stability of the entire grid system, increasing the risk of low-frequency oscillations and dynamic stability problems in the ultra-large power grid. Simultaneously, the hysteresis characteristics of the generator field windings and fast excitation systems further worsen the damping characteristics between the generator and the grid, increasing the risk of active low-frequency oscillations between the generator and the grid.

[0003] Power System Stabilizers (PSS), as an additional control function for generator excitation regulation, compensate for the generator's uncompensated lag characteristics by superimposing a PSS output with a phase leading the speed change at the excitation system voltage setpoint. This increases damping and suppresses low-frequency active power oscillations. Because the principle of PSS suppression of low-frequency active power oscillations is clear and easy to implement, it has become the most widely used, most effective, and most economical means of damping low-frequency active power oscillations in engineering applications.

[0004] The most widely used PSS currently is the PSS-2B power system stabilizer, which boasts strong oscillation suppression capabilities, ease of on-site setting tests, and resistance to reverse regulation. The input signal for the PSS-2B stabilizer model uses a combination of active power and generator speed. The model block diagram is shown below. Figure 1 As shown, the PSS-2B model essentially constructs a change in mechanical power ΔP based on the interrelationship between mechanical power, active power, and rotational speed. M According to the generator rotor motion equation, the relationship between the change in rotational speed and the changes in mechanical power and electromagnetic power is shown in the following equation:

[0005] ΔP M -ΔP e =T J sΔω

[0006]

[0007] When low-frequency active power oscillations occur during generator operation, the average value of active power (electromagnetic power) remains unchanged, and the mechanical power P input to the prime mover... MIt will not change, i.e., ΔP M If the acceleration power (ΔP) is approximately equal to 0, then the acceleration power (ΔP) M -ΔP e This is the change in active power -ΔP e (Active power is deceleration power). In the PSS-2B model, the change in active power is lags by 90 degrees after being processed by the power-frequency conversion stage and then amplified by the coefficient K3 (K3=1). This amplified change is then superimposed on the change in rotational speed to obtain the fitted change in mechanical power, which is essentially equal to 0. After passing through a notch filter, the change in active power is subtracted to obtain the change in acceleration power. The phase of the acceleration power is close to the phase of the rotational speed signal Δω. Then, a third-order lead-lag stage is used to compensate for the lag characteristics of the excitation system, so that the torque provided by the PSS is near the Δω axis, producing a good additional positive damping effect.

[0008] When the generator needs to change its output active power (i.e., the prime mover normally adjusts the input mechanical power), the change in the grid-connected generator speed Δω is very small (Δω is approximately equal to 0, mainly reflected in the change of the power angle δ), so the change in mechanical power ΔP M Approximately equal to the change in active power ΔP e If the acceleration power is approximately zero, the PSS-2B output value is almost zero, thus possessing a good "anti-reverse regulation" function (reactive power reverse regulation refers to the phenomenon that the generator reactive power will change significantly when the prime mover increases or decreases the active power in the early PSS-1A model).

[0009] However, if the active power oscillates due to issues with the prime mover's speed control system, the frequent fluctuations in the opening of the main steam valve or guide vane controlled by the governor cause periodic oscillations in the prime mover's input mechanical power (referred to as forced oscillation caused by the governor). Consequently, both the generator's output power and speed exhibit periodic fluctuations, and the change in mechanical power ΔP... M Change in active power - ΔP eThe change in rotational speed Δω is not equal to 0. At this time, the change in active power in the PSS-2B model, after lagging by 90 degrees, is superimposed with the change in rotational speed. The resulting fitted mechanical power change is not equal to 0, but fluctuates periodically. The fitted mechanical power of this fluctuation produces phase shift and amplitude change after passing through the notch filter. The magnitude of the phase shift is related to the fluctuation frequency. The fitted power after this filtering is no longer the mechanical power value in the strict sense of equation (1). The power change obtained by subtracting it from the original change in active power is no longer the acceleration power change in the strict sense. Moreover, the phase of this "acceleration power" will be significantly offset from the phase of the rotational speed signal Δω. The phase angle of the offset is related to the fluctuation frequency. Finally, after passing through the third-order lead-lag link and the PSS additional torque generated by the lag of the excitation system, the phase becomes uncertain. At this time, the effect of the PSS output may produce positive damping to suppress the active power fluctuation of forced oscillation, or it may produce negative damping to exacerbate the active power fluctuation of forced oscillation. Therefore, when the speed control system causes forced oscillations, the magnitude and phase of the additional torque provided by the PSS-2B model vary with the forced oscillation frequency and amplitude. The additional damping effect generated by PSS-2B is uncertain and may provide negative damping, thereby exacerbating active power oscillations and posing a risk to the safe and stable operation of the unit.

[0010] In power systems, cases of forced oscillations in active power generation caused by governor malfunctions are frequent, potentially inducing oscillations in neighboring units and leading to regional low-frequency grid oscillations. Therefore, there is an urgent need to design a Power Stability System (PSS) stabilizer model that can not only provide positive damping torque during natural generator-grid oscillations and exhibit good anti-reverse regulation performance, but also provide clear and effective positive damping during forced oscillations caused by governors, thus preventing exacerbation of active power fluctuations caused by forced oscillations. Summary of the Invention

[0011] Purpose of the invention: The purpose of this invention is to provide a method for realizing a power system stabilizer that enhances the damping effect during power forced oscillation by using the changes in generator active power and speed to obtain a power-speed composite signal Upe-ω, and then passing it through a lead-lag stage.

[0012] Technical solution: The power system stabilizer implementation method of the present invention includes the following steps:

[0013] S1 measures the generator speed signal ω, which, after passing through a speed measurement compensation circuit and a speed DC blocking circuit, yields the speed change Δω, and is then processed by the speed signal gain coefficient K. w The speed change vector signal Δω is obtained after amplification and low-pass filtering. in ;

[0014] S2 measures the generator's active power signal Pe. After passing through a power measurement compensation stage and a power DC blocking stage, the power change ΔPe is obtained. Then, after passing through a power-frequency conversion stage and a low-impedance filtering stage, the active power change vector signal ΔPe is obtained. in ;

[0015] S3, the rotational speed change vector signal Δω obtained in step S1 in and the active power change vector signal ΔPe obtained in step S2 in Adding them together, we obtain the power-speed composite signal Upe-ω;

[0016] S4. The power-speed composite signal Upe-ω obtained in step S3 is processed by a third-order lead-lag correction circuit, Kpss proportional amplification, and upper and lower limits, and then used as the output of the power system stabilizer.

[0017] Furthermore, the calculation of the change in rotational speed Δω in step S1 is as follows:

[0018]

[0019] Where T5 is the time constant of the measurement compensation circuit; T w1 T is the time constant of the first DC blocking element of the speed signal. w2 The time constant of the second DC blocking element of the speed signal; s represents the differential operator;

[0020] Rotational speed change vector signal Δω in The calculation is as follows:

[0021]

[0022] Among them, K w is the gain coefficient of the speed signal; a1 and b1 are the coefficients of the low-pass filter.

[0023] Furthermore, the power change ΔPe in step S2 when using a two-order power DC blocking element is calculated as follows:

[0024]

[0025] Alternatively, the power change ΔPe can be calculated using a first-order power DC blocking element as follows:

[0026]

[0027] Where T6 is the time constant of the active power measurement compensation circuit; T w3 T is the time constant of the first DC blocking element of the active signal. w4 The time constant of the second DC blocking element of the active signal; s represents the differential operator;

[0028] Power change vector signal ΔPein The calculation is as follows:

[0029]

[0030] Among them, K p denoted as the gain coefficient of the power frequency conversion stage of the power signal, T7 as the time constant of the power frequency stage; a1 and b1 are the coefficients of the low-pass filter, a2 and b2 are the coefficients of the low-impedance filter; s represents the differential operator.

[0031] Furthermore, the calculation of the power-speed composite signal Upe-w in step S3 is as follows:

[0032] U Pe-ω =Δω in +ΔP ein

[0033] Where, Δω in The speed change vector signal, ΔPe in This is a power change vector signal.

[0034] Compared with the prior art, the significant effects of this invention are as follows: 1. This invention synthesizes the speed-power composite signal by passing the speed change and the active power change through low-pass filtering and low-impedance filtering respectively, and then uses it as the PSS output after passing through the lead-lag correction stage. When the active power forced oscillation occurs in the speed regulation system, the effective positive damping is mainly generated by the filtered speed change, avoiding the negative damping effect that may be brought about by the existing PSS-2B model, which exacerbates the active power fluctuation.

[0035] 2. When the machine-grid natural damping oscillation occurs, the phase of the power-speed synthesized signal Upe-ω of this invention is basically close to the phase of the speed signal Δω, which can produce an additional positive damping effect similar to that in the PSS-2B model, and has a good anti-reverse modulation effect.

[0036] 3. When the speed regulator normally adjusts the mechanical power, the power-speed synthesis signal Upe-ω of this invention is basically zero, and the PSS model output is almost zero, which has good anti-reverse regulation capability. Attached Figure Description

[0037] Figure 1 Here is a block diagram of the existing power system stabilizer PSS-2B model, where K S1 K S2 K S3 For PSS gain, T W1 T W2 T W3 T W4 The time constants of the PSS DC blocking circuit are T1, T2, T3, T4, T6, T7, and T. 10 T 11U is the PSS time constant, M, N, T8, and T9 are the PSS notch filter parameters, and U is the PSS time constant. SSmax U SSmin Set the PSS output limiting value;

[0038] Figure 2 This is a block diagram of the PSS model of the present invention;

[0039] Figure 3 This is a typical phase-amplitude frequency response curve of the speed-varying low-pass filter of the present invention;

[0040] Figure 4 This is a typical phase-amplitude frequency response curve of the power-varying low-impedance filter of the present invention. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0042] like Figure 2 The diagram shown is a block diagram of the power system stabilizer model of the present invention, and its implementation steps are as follows:

[0043] Step 1: Measure the generator speed signal ω. After passing through the speed measurement compensation stage and the two-stage DC blocking stage, obtain the speed change Δω. After passing through the speed signal gain coefficient Kw amplification stage and the low-pass filtering stage, obtain the speed change vector signal Δωin.

[0044] The change in rotational speed Δω is calculated using the following formula (1):

[0045]

[0046] Wherein, T5 is the time constant of the speed measurement compensation circuit, which is set according to the deviation between the time constants of speed measurement and active power measurement; T w1 T is the time constant of the first DC blocking element of the speed signal. w2 is the time constant of the second DC blocking element of the speed signal; s represents the differential operator.

[0047] The measurement time constant represents the time it takes for the effective measured value of a certain analog quantity to reach 63.2% of the final measured value, indicating how quickly the measurement result is obtained. Since the time constants for speed measurement and active power measurement may differ, a measurement compensation circuit is set to compensate for the difference in measurement time constants. For example, if the time constant for measuring active power is 30ms and the time constant for measuring speed is 20ms (meaning active power measurement is slower than speed measurement), then the time constant for the speed measurement compensation circuit should be set to T5 = (30-20)ms = 10ms. Conversely, if the time constant for measuring active power is 20ms and the time constant for measuring speed is 30ms (meaning speed measurement is slower than active power measurement), then the time constant for the active power measurement compensation circuit should be set to T6 = 10ms.

[0048] Rotational speed change vector signal Δω in The calculation is shown in equation (2):

[0049]

[0050] Among them, K w The gain coefficient of the speed signal is used to change the amplitude of the speed change Δω so that the magnitude of the speed change is equal to the magnitude of the active power Pe after the power blocking link and power frequency conversion, that is, it satisfies the relationship of the following equation (3), and the mechanical power used for fitting the equivalent is 0.

[0051]

[0052] a1 and b1 are the coefficients of the low-pass filter. The speed change signal Δω, after being passed through the low-pass filter, reduces high-frequency noise and increases the signal-to-noise ratio. T7 is the time constant of the power signal frequency stage. A typical phase-amplitude-frequency response curve of the low-pass filter is shown below. Figure 3 As shown.

[0053] Step 2: Measure the generator active power signal Pe. After passing through a first-order measurement compensation circuit and a second-order or first-order DC blocking circuit, obtain the power change ΔPe. Then, after passing through a power-frequency conversion circuit and a low-impedance filtering circuit, obtain the active power change vector signal ΔPein.

[0054] The change in active power can be calculated using either a two-order DC blocking element or a one-order DC blocking element. The calculation of the power change ΔPe using a two-order DC blocking element is shown in equation (4), and the calculation of the power change ΔPe using a one-order DC blocking element is shown in equation (5).

[0055]

[0056]

[0057] Among them, T6 is the time constant of the active power measurement compensation circuit, which needs to be set according to the time constant deviation between active power measurement and speed measurement; T w3 T is the time constant of the first DC blocking element of the active signal. w4 is the time constant of the second DC blocking element of the active signal; s represents the differential operator.

[0058] Power change vector signal ΔPe in The calculation is shown in the following formula (6):

[0059]

[0060] Among them, K p The gain coefficient of the power-frequency conversion stage is used to change the amplitude of the power change ΔPe so that the magnitude of the active power Pe after passing through the power blocking stage and the power-frequency conversion stage is equal to the magnitude of the speed change, which satisfies the relationship of equation (3) in step one.

[0061] a2 and b2 are the coefficients of the low-impedance filter. After power-frequency conversion and low-impedance filtering, the power change signal ΔPe significantly attenuates the active power change in the low-frequency range. A typical phase-amplitude frequency response curve of the above low-impedance filter is shown below. Figure 4 As shown.

[0062] Step 3: Add the speed change vector signal Δωin obtained in Step 1 and the active power change vector signal ΔPein obtained in Step 2 to obtain the power-speed composite signal Upe-ω. The calculation of the power-speed composite signal Upe-ω is shown in Equation (7):

[0063] U Pe-ω =Δω in +ΔP ein (7).

[0064] Step four: The synthesized signal Upe-ω obtained in step three is processed by a third-order lead-lag compensation stage, Kpss proportional amplification, and upper and lower limits, and then used as the output of the power system stabilizer. The parameters of the third-order lead-lag compensation stage are set according to the synthesized signal Upe-ω and the lag characteristics of the excitation system; for self-excited excitation systems, only a first-order or second-order lead-lag stage may be set, while for three-machine excitation systems, a third-order lead stage may be required.

[0065] Depend on Figure 4 It can be seen that after power-frequency conversion and low-impedance filtering, the power change vector signal ΔPe at an oscillation frequency below 0.5Hz is... inThe output attenuation is significant; the low-impedance filter has a significant attenuation effect on low-frequency signals. Specifically, when the oscillation frequency is 0.01Hz to 0.1Hz, the filter output amplitude is less than 0.3% of the input; when the oscillation frequency is 0.1Hz to 0.5Hz, the filter output amplitude is less than 7% of the input. This results in a significant attenuation of the active component in the synthesized signal Upe-w below the oscillation frequency of 0.5Hz, with the speed filtering signal becoming dominant. Practical engineering shows that the forced oscillations caused by the speed governor are all low-frequency oscillations, with the forced oscillation frequency generally not higher than 0.5Hz. Therefore, under the forced oscillation caused by the speed governor, the power-speed synthesized signal Upe-w mainly contains the speed filtering signal, whose phase is close to the speed Δω axis. Therefore, after the third-order lead-lag element compensates for the lag characteristics of the excitation system, the PSS provides torque near the Δω axis, thus providing a clear and effective positive damping effect. During machine-grid natural damping oscillations, the change in mechanical power is zero. The power-speed composite signal Upe-ω, synthesized from the speed change vector signal Δωin and the active power change vector signal ΔPein, mainly contains the acceleration power change. The phase of the acceleration power is approximately close to the phase of the speed signal Δω. After a third-order lead-lag compensation element compensates for the lag characteristics of the excitation system, the torque provided by the PSS is near the Δω axis, producing a good additional positive damping effect. When the prime mover adjusts the mechanical power at a normal rate, the speed change Δω is approximately zero, and the speed change vector signal Δω... in It is also approximately equal to 0, and at this time the active power changes slowly. After low-impedance filtering, the power change vector signal ΔPe in Approximately equal to 0, the power-speed synthesis signal Upe-ω is basically zero, and the PSS model output is almost zero, thus possessing good "anti-modulation" function.

[0066] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for implementing a power system stabilizer that enhances the damping effect of power forced oscillation, characterized in that, Includes the following steps: S1 measures the generator speed signal ω, which, after passing through a speed measurement compensation circuit and a speed DC blocking circuit, yields the speed change Δω, and is then processed by the speed signal gain coefficient K. w The speed change vector signal Δω is obtained after amplification and low-pass filtering. in ; S2 measures the generator's active power signal Pe. After passing through a power measurement compensation stage and a power DC blocking stage, the power change ΔPe is obtained. Then, after passing through a power-frequency conversion stage and a low-impedance filtering stage, the active power change vector signal ΔPe is obtained. in ; S3, the rotational speed change vector signal Δω obtained in step S1 in and the active power change vector signal ΔPe obtained in step S2 in Adding them together, we obtain the power-speed composite signal Upe-ω; S4. The power-speed composite signal Upe-ω obtained in step S3 is processed by a third-order lead-lag correction circuit, Kpss proportional amplification, and upper and lower limits, and then used as the output of the power system stabilizer.

2. The method for implementing a power system stabilizer with enhanced power forced oscillation damping effect according to claim 1, characterized in that: The calculation of the change in rotational speed Δω in step S1 is as follows: Where T5 is the time constant of the measurement compensation circuit; T w1 T is the time constant of the first DC blocking element of the speed signal. w2 The time constant of the second DC blocking element of the speed signal; s represents the differential operator; Rotational speed change vector signal Δω in The calculation is as follows: Among them, K w is the gain coefficient of the speed signal; a1 and b1 are the coefficients of the low-pass filter.

3. The method for implementing a power system stabilizer with enhanced power forced oscillation damping effect according to claim 1, characterized in that: The power change ΔPe in step S2 when using a two-order power DC blocking element is calculated as follows: Alternatively, the power change ΔPe can be calculated using a first-order power DC blocking element as follows: Where T6 is the time constant of the active power measurement compensation circuit; T w3 T is the time constant of the first DC blocking element of the active signal. w4 The time constant of the second DC blocking element of the active signal; s represents the differential operator; Power change vector signal ΔPe in The calculation is as follows: Among them, K p denoted as the gain coefficient of the power frequency conversion stage of the power signal, T7 as the time constant of the power frequency stage; a1 and b1 are the coefficients of the low-pass filter, a2 and b2 are the coefficients of the low-impedance filter; s represents the differential operator.

4. The method for implementing a power system stabilizer with enhanced power forced oscillation damping effect according to claim 1, characterized in that, The calculation of the power-speed composite signal Upe-ω in step S3 is as follows: U Pe-ω =Here in +ΔP ein Where, Δω in The speed change vector signal, ΔPe in This is a power change vector signal.

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