KR100298867B1 - Method for enhancing the damping of the generator and stabilizing the frequency control system by using a modified PID control - Google Patents

Abstract

The present invention relates to a method for improving the stabilization of a frequency control system and the damping of a generator by a modified PID control method. In response to the frequency deviation multiplied by the frequency feedback gain constant (1 / R) (S1), proportional control is performed with the proportional feedback gain constant K _p = 1 (S2), and the integral control is performed with the integral feedback gain constant (K _I ). (S3) execute derivative control with the differential feedback gain constant (K _D ) and (S4) the derivative of the position displacement of the valve ( Providing; In a governor with a non-wind-up limiter, check X _GV = X _GVMAX and -X _GV + P _c 0 (S5) _{.If the} condition is not satisfied, check X _GV = X _GVMIN and -X _GV + P _c <0 (S6). ) If the condition is not met Model the governor with (S7) and satisfy the conditions of S5 and S6 Modeling the governor with = 0 (S8) to provide a positional displacement ΔX _GV of the steam valve; Turbine modeling step (S9); Power generation amount ΔP _m output step S10; Providing a ΔP _m −ΔP _D by receiving a load demand amount ΔP _D (S11); Generator modeling step (S12); And frequency deviation [Delta] [omega] output step S13.

Description

Method for enhancing the damping of the generator and stabilizing the frequency control system by using a modified PID control}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for enhancing damping of a generator by a modified PID frequency control system. In particular, in the generator governor control, a differential signal of frequency is fed back and used as a control input so that the damping effect of the generator is used. The present invention relates to a method for improving the stabilization and damping of a generator by a modified PID control method.

In general, various methods have been proposed as a control method of a conventional frequency controller, but generally, a control method adopted by a power plant can be generally classified into two methods. The first method is a simple feedback control method in which only the frequency deviation is fed back. The second method is an integral control method in which the frequency deviation and frequency deviation integrated values are fed back using an appropriate gain constant.

1 is a block diagram showing a conventional frequency control system. The frequency control system of the integral control method adopts the control method as shown in Fig. 1, and its response characteristic is the frequency feedback gain. The root locus of the change in can be easily identified. Disturbance due to load fluctuations acting as input variables in the block diagram above And frequency deviation Calculating the open loop transfer function between them is given by the following equation (1).

The frequency feedback gain If the open loop transfer function is modified to determine the response characteristics of the control system, the characteristic equation of the frequency controller system is given by Equation (2).

Frequency feedback gain in the above equation When transformed into the characteristic equation for, the following equation (3) is obtained.

New open loop transfer function from Equation (4) You can get the transfer function is the original transfer function It has a root locus with the same characteristics as

2 is about It represents the root locus according to the change of. At this time, the generator parameters used are shown in Table 1.

Inertia constant H 5 Governor time constant T _H 0.1 s Damping factor D 2 p.u Turbine time constant T _T 10s frequency f 60 Hz Integral feedback gain constant K _T 20 / ω _s Regulation R 0.05 Differential feedback gain constant K _D 50 / ω _s

Figure 2 (a) is when the integral control circuit is included Figure 2 (b) is the root locus of the conventional frequency control system when the integral control circuit is not included.

As shown in FIG. 2, there is a risk that the system may become unstable even with a small change in speed regulation R in any of the control schemes. Because of this, the adjustment of R value is limited and is usually set to 5. If the operator operates with the R value set to 1, the system stability can be guaranteed but long oscillation will occur, which further restricts the adjustment of R.

Speed governor control technology has been developed from the control of hydro generators, and the results are being used in thermal power generators. In order to keep the frequency constant in the generator control, the frequency deviation of the generator ) And its integral value ( ), Generator terminal voltage deviation ( ), Female winding ), The control method as shown in FIG. 1 has been generally used by only feeding back a), thereby ensuring that a complete generator control structure can be provided.

On the other hand, some have studied the method of using differential signal of frequency as a control input variable by introducing PID control theory. However, this suggests that this undermines the system stability. It's happening.

Therefore, in order to obtain a generator damping effect, a control loop called a power system stabilizer (PSS) is devised and used.

However, although the governor can be used as a control means to effectively control the energy accumulated in the system, which is the main cause of system fluctuations in case of failure, the existing governor cannot be practically utilized due to the mechanical limitation of the steam valve and the constraint of the feedback gain constant range. Situation. Conventional generator damping effect is to use the power system stabilizer (PSS) to input the input signal to the exciter side, but the control loop (loop) of the exciter system has a time constant T _do ^' Because the response is very large, the response is very late so that a large effect is not obtained.

Currently, there is no way to effectively obtain generator damping, so long-term oscillation, inter-area oscillation, and low frequency oscillation in most systems There was a disadvantage that could not be solved. As well as frequency deviations, Increasing the feedback gain of the system may cause the system to become unstable.

An object of the present invention has been proposed to solve the above problems of the prior art, by introducing a modified PID control including a differential control loop to the generator frequency control system to significantly improve the generator damping effect, In the frequency control of the method, if the frequency feedback gain is increased, the system may become unstable, but stability is always guaranteed regardless of the increase or decrease of the gain, so that it corresponds to the voltage compensator loop in the frequency control system. It can be used as a frequency stabilizer (stabilizer) that can play a role, and the stabilization and generator of the frequency control system by a modified PID control method to achieve the overall system stabilization by improving the damping effect of the individual generator Provides a way to promote damping.

1 is a block diagram showing a conventional frequency control system.

Figure 2 (a) is when the integral control circuit is included Figure 2 (b) is a root locus diagram for a conventional frequency control system when the integral control circuit is not included.

3 is a block diagram showing a PID frequency control system according to the present invention.

4 is a (a) mechanical structure (b) block diagram of a modified steam valve system;

5 is the root locus (K _I = 0) for the frequency controller proposed in FIG.

6 (a) to 6 (b) show the root locus (K _I ≠ 0) for the frequency controller proposed in FIG.

7 (a) to 7 (b) show the root locus for the integral feedback gain constant.

8 (a) to 8 (c) show the steam valve position limiter and the mechanical structure.

9 is a frequency response of a Mechanical Hydraulic Control (MHC) governor.

10 is a schematic diagram of a four-phase 10 busbar (Kundur system).

11 is a frequency (ω), electrical output (P _e ) response of generator # 4 of FIG. 10.

12 (a) is a frequency response according to the speed regulation constant R value of the PID frequency controller proposed in the present invention and Figure 12 (b) is a conventional PI controller.

FIG. 13 is a frequency (ω), electrical output (P _e ) response of generator # 2 of FIG. 10.

14 is a frequency response according to the governor speed regulation R value.

15 is a flowchart illustrating a method for enhancing damping of a generator by a PID frequency control system proposed in the present invention.

Explanation of symbols on the main parts of the drawings

H: Inertia constant D: Damping coefficient

f: frequency R: speed regulation

T _H : governor time constant T _T : turbine time constant

K _D : differential feedback integration constant K _{D, crit} : critical differential feedback integration constant

K _I : Integral feedback integration constant K _{I, crit} : Critical integral feedback integration constant

ΔX _GVmax : Maximum position of the valve ΔX _GVMIN : Minimum position of the valve

ΔX _GV : Positional displacement of valve ΔP _D : Disturbance

ΔP _m : mechanical power

Δω: frequency deviation P ₁ , P ₂ , P ₃ , P ₄ : pole

Z ₁ , Z ₂ , Z ₃ : Zero

PID: Proportional and Integral and Derivative

In order to achieve the above object, the present invention receives feedback of a frequency deviation multiplied by a frequency feedback gain constant (1 / R), which is an inverse of the speed governor speed control constant (R) (S1). The proportional control is executed by the constant K _p = 1 (S2), the integral control is performed by the integral feedback gain constant (K _I ) (S3) and the derivative control is performed by the differential feedback gain constant (K _D ) ( S4) Control input for adjusting valve position by adding up Providing; For modeling the steam valve position limit, it is checked if the position displacement (X _GV ) of the steam valve is the maximum value (X _GV = X _GVMAX ) and -X _GV + P _c 0 (S5). If the displacement (X _GV ) is the minimum value (X _GV = X _GVMIN ) and -X _GV + P _c <0 (S6), check the steam valve position (T _H : governor time constant, P _c : position adjuster) (S7), and satisfy the conditions S5 and S6 By modeling the governor with = 0 (S8), the nonwindup limiter can accurately model the mechanical structure of the valve reciprocating within the upper and lower limits, providing a positional displacement (ΔX _GV ) of the steam valve. step; A turbine modeling step (S9) first approximated by (T _T : turbine time constant, P _m : mechanical power); Outputting a generation amount ΔP _m (MW) (S10); Providing a ΔP _m -ΔP _D by receiving a load requirement ΔP _D corresponding to the disturbance (S11); Generator kinematic equation (D: damping coefficient, P _D : disturbance) modeling a generator using a swing equation to improve the damping effect of the generator to achieve stabilization of the system (S12); And a step (S13) of feeding back and outputting the frequency deviation (Δω) for stabilizing the system quickly, and providing a method for improving the stabilization of the frequency control system and damping of the generator by the modified PID control method.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. The present invention proposes a method of dramatically improving the damping effect of a generator by feeding back a frequency differential signal in a speed governor control.

3 is a block diagram showing a modified PID frequency control system according to the present invention.

Referring to FIG. 3, in the modified PID frequency control system, the stable region gains the output of a flyball speed governor in view of the fact that the stability region depends on the ratio between gains rather than the magnitude of each feedback gain. It has a modified PID control structure that gives a constant, then derivatives, integrates and feeds back.

The modified PID controller feeds back the differential signal of the frequency to ensure that all poles of the system are located in the left half of the frequency plane, ensuring a wide range of stable areas. It is possible to widen the operation range of the frequency feedback gain constant which is normally set by setting 5.

4 shows (a) mechanical structure and (b) block diagram of a modified steam valve system. Referring to FIG. 4, since the steam valve reciprocates in a large range for a large disturbance, the control performance is considered after modeling in consideration of the constraint of the valve position. Simulation results reflecting the modified PID controller and steam valve position limitations show that the damping of the generator is significantly improved.

Existing frequency controllers allow the feedback gain constants to be adjusted individually. However, noting that the ratio between constants contains more information than the magnitude of these constants, a new frequency controller with a modified PID controller with differential and integral feedback circuits is proposed.

Referring to Fig. 3, the novel PID frequency controller according to the present invention is a frequency controller that is guaranteed to have frequency control stability over a wide range of feedback gain constants.

It should be noted that the feedback signal can be easily obtained by measuring the flyball output of the speed governor, and the differential and integral feedback circuits can also be easily implemented.

When not including CASE 1 integral control circuit ( )

The open loop transfer function for this case is expressed by the following equation (5).

The root locus is shown in FIG. 5 using the root locus tool in MATLAB for the frequency controller using the generator parameters of Table 1. 5 (a) is Indicates the root locus. When the number of poles is N _p and the number of zeros is N _z , the angles of the asymptotes (θ ₀ , θ ₁ ), the intersection with the real axis (σ _A ) and the branching point (σ _c ) are calculated as follows: do.

Real axis and intersection:

Junction:

5 (b) shows Indicates the root locus. When the number of poles is N _p and the number of zeros is N _z , the angles of the asymptotes (θ ₀ , θ ₁ ), the intersection with the real axis (σ _A ) and the branching point (σ _c ) are calculated as follows: do.

Real axis and intersection:

Junction:

Note that the pole here And zero This is an unusual case of offsetting each other.

As shown in Fig. 5, all asymptotes intersect the real axis perpendicularly to the left half of the s-plane. From this it is possible to add a differential feedback loop to prevent the root locus from moving to the right side. Comparing the root locus of FIG. 5 and the root locus of FIG. 2, it can be seen that the system stability can be absolutely guaranteed no matter what the speed regulation R has. Where differential feedback gain constant Has a big impact on the stability of the system.

if, 5, the asymptote of FIG. 5 gradually shifts to the right, and a critical differential feedback gain constant, which is a critical value. With respect to the asymptotes will be coincident with the imaginary axis. The critical differential feedback gain constant The value can be calculated as in Equation (8) below.

The critical differential feedback gain constant Is the minimum margin to ensure stability. Therefore, in order to ensure the stability of the system, the differential feedback gain constant At least the critical differential feedback gain constant It must be set to a larger value.

When the CASE 2 integral control circuit is included ( )

The open loop transfer function for this case is

The root locus for the transfer function of Equation (9) is shown in FIG. 6 using the generator parameters of Table 1. FIG. 6 (a) and 6 (b) show the root locus (K _I ≠ 0) for the frequency controller proposed in FIG. In this case, the differential and integral feedback loop adds one pole and two zeros to the simple feedback system so that no root of the system moves to the right half.

As mentioned in CASE 1, system stability is the differential feedback gain constant. Mainly depends on the value of. The differential feedback gain constant As the decreases, the vertical asymptotes move to the right, making the system unstable. The differential feedback gain constant that can guarantee absolute stability for all governor speed regulation R values Is calculated as Equation (10).

Where system stability is the integral feedback gain constant It also depends on. If the integral feedback gain constant If becomes large, for example The root locus is moved to the right as shown in FIG. 7 and the system becomes unstable. Likewise, the integral feedback gain constant to ensure absolute stability for all governor speed control constants R values. Is the critical value of the critical integral feedback gain constant You must choose a smaller one. The critical integral feedback gain constant Can be calculated as follows by the Routh-Hurwitz method.

In conclusion, in the PID frequency controller according to the present invention including an integral control circuit, the differential feedback gain constant The critical differential feedback gain constant Select a larger value and the integral feedback gain constant The critical integral feedback gain constant Selecting a smaller value will ensure absolute stability.

On the other hand, the consideration about a steam valve position is demonstrated next. Valve position limiting modeling should be carefully handled in Mechanical Hydraulic Control (MHC) governor modeling. When large disturbances occur, valve position limit modeling has a large impact on widespread and long lasting fluctuation control.

The valve position limit can be largely modeled as a windup limiter and a nonwindup limiter. As a result of analyzing the control effect of the frequency fluctuation problem in both cases, it was concluded that the Nonwindup Limiter had the best control performance.

8 shows each case of the valve position limiting model. 8 (a) to 8 (c) show a steam valve position limiter and a mechanical structure, FIG. 8 (a) shows a windup limiter, FIG. 8 (b) shows a nonwindup limiter, and Fig. 8 (c) shows the mechanical structure of a piston-like valve system. Fig. 8 (a) shows a windup limiter. There is some error in modeling the mechanical structure as shown in Fig. 8 (c) due to the feedback of the signal. The nonwindup limiter as shown in FIG. 8B accurately corrects the error and accurately reflects the mechanical structure of FIG. 8C. Derivation of the state equation for the nonwindup limiter is as follows.

In order to find out the difference between the two models, the simulation was applied to the Kundur 4th 10 bus system. The model system is shown in FIG. 10 and the frequency response is obtained when the proposed PID frequency controller is installed in the mechanical hydraulic control (MHC) governor of generator # 4 when a three-phase short circuit occurs in bus # 9. It was.

As shown in FIG. 9, the nonwindup limiter shows better control performance than the windup limiter. Therefore, in the present invention, a simulation using a nonwindup limiter was performed.

The modified PID frequency controller according to the present invention is applied to a power system to examine the effect of the damping effect of the differential feedback loop on the system, and to describe the stability change according to the change of the system parameter. As the sample strains, the Kundur 4th 10 busbar strain and the New England 39Bus strain were selected.

(1) Kundur four 10 bus system

Each generator is a round-rotor synchronous machine Modeled as a model. Referring to FIG. 10, generator # 1 is equipped with a self-excited DC exciter, and the remaining generator (G) is equipped with a thyristor exciter and is seen only in generator # 4. The PID frequency controller proposed in the present invention is installed.

In order to assume a large disturbance, a three-phase ground fault occurred in mothership # 9 for 0.1 second. In order to observe the performance of the proposed PID frequency controller, a power system stabilizer (PSS) and a conventional proportional derivative (PI) controller are installed. FIG. 11 shows the frequency ω, electrical output _Pe response of generator # 4 of FIG. It can be seen that the proposed controller from FIG. 11 significantly improves system damping than the power system stabilizer (PSS) or the existing PI controller.

Parameter / Controller The present invention existing Speed Regulation R 5 5 Differential feedback gain constant K _D 0.3 0.0 Integral feedback gain constant K _I 0.2 20.0

(2) Effect of governor speed regulation R

Frequency Feedback Gain Constant in Conventional Controllers If is increased, the system becomes unstable, so that there is a significant restriction on the regulation range of the governor speed regulation R and is usually set at 5. The modified PID frequency controller of the present invention ensures system stability against any governor speed regulation R.

The frequency response is shown in FIG. 12 when the value is changed to 5, 1, 0.1 to determine the effect of the governor speed regulation R on the modified PID frequency controller and the existing controller according to the present invention. 12 (a) shows the PID frequency controller proposed in the present invention and Figure 12 (b) shows the frequency response according to the governor speed control constant R value of the conventional PI controller.

Referring to FIG. 12 (a), the PID frequency controller proposed in the present invention can confirm that system damping increases as the governor speed control constant R decreases. Referring to FIG. 12 (b). In this case, the existing PI controller can confirm that the shaking of the system is increasing as the R value decreases. In the root locus analysis, in the PID frequency controller proposed in the present invention, since all system poles are located on the left half of the s plane, the system is stabilized with respect to the governor speed regulation constant R value. On the other hand, in the conventional controller, as the R value decreases, the system poles move toward the right half surface, and the fluctuation increases.

(3) New England 39 Mothership System

The PID frequency controller proposed in the present invention is applied to the New England 39 bus system to measure the performance. Each generator is modeled as a two-axis model and all generators except generator # 1 are equipped with an IEEE Type 1 exciter.

To assume a large disturbance, a three-phase short circuit accident in bus # 6 was assumed to occur for 0.1 second. The short circuit accident makes the generator near the accident point unstable and causes outage with other generators in the system.

Therefore, the proposed controller was installed in generator # 2 near the accident site, and also mounted on generators # 1, # 3, # 7, and # 9. The frequency (ω) and electrical output (P _e ) responses of generator # 2 for the PID frequency controller and the conventional controller proposed in the present invention are shown in FIG. 13. In order to examine the effect of the governor speed regulation R on the modified PID frequency controller (FIG. 3) and the conventional frequency controller (FIG. 1) according to the present invention, the frequency response was changed to 5 and 10.1. 14 is shown. 14 shows the frequency response according to the governor speed regulation R value.

Referring to FIG. 14, as the governor speed control constant R decreases, the PID frequency controller according to the present invention greatly increases system damping.

As a result, the PID frequency controller proposed in the present invention can be utilized as a useful means for improving system damping in place of the conventional power system stabilizer (PSS), and the characteristics of the frequency controller according to the present invention. Unlike the power system stabilizer (PSS), a complicated parameter tuning process is not required.

15 is a flowchart illustrating a method of enhancing damping of a generator by a PID frequency control system. A feedback of the frequency deviation obtained by multiplying the frequency feedback gain constant (1 / R), which is the inverse of the speed governor speed control constant (R), is fed back (step S1), proportional to the proportional feedback gain constant K _p = 1. The control is executed (step S2), the integral control is executed by the integral feedback gain constant K _I (step S3) and the differential control is executed by the differential feedback gain constant K _D (step S4) and summed Control input for position adjustment ). For modeling the steam valve position limit, check whether the position displacement (X _GV ) of the steam valve is the maximum value (X _GV = X _GVMAX ) and -X _GV + P _c 0 (step S5). If the position displacement (X _GV ) is at the minimum value (X _GV = X _GVMIN ) and -X _GV + P _c <0 (step S6), then the steam valve position is (T _H : governor time constant, P _c : position control input) (step S7), and the conditions S5 and S6 are satisfied. By modeling the governor with = 0 (S8) and modeling it with a nonwindup limiter that can accurately model the mechanical structure of the valve reciprocating within the upper and lower limits, it provides a positional displacement (ΔX _GV ) of the steam valve. . (T _T : Turbine time constant, P _m : Mechanical power) approximates the first-order turbine modeling (step S9), outputs power generation (ΔP _m ) (MW) (step S10) and corresponds to disturbance The load demand ΔP _D is applied to provide ΔP _m −ΔP _D (step S11). Generator kinematic equation (D: Damping Coefficient, P _D : Disturbance) Model the generator using Swing Equation to improve the damping effect of the generator to achieve system stabilization (step S12) and to stabilize the system quickly. The frequency deviation Δω is fed back and output (step S13).

Therefore, the method of improving the stabilization of the frequency control system and the damping of the generator by the modified PID control method according to the present invention ensures stability at a wide range of frequency feedback gain, and the damping effect of the generator Stabilization of the entire system can be achieved by increasing.

As described above, the method of improving the stabilization of the frequency control system and the damping of the generator by the modified PID control method according to the present invention ensures stability at a wide range of frequency feedback gain, and the damping of the generator ( Stabilization of the entire system is achieved by increasing the damping effect, and it provides a means to effectively control the surplus energy accumulated in the system in the event of a failure. It can be used as a frequency stabilizer that can serve as a voltage compensator loop in a frequency control system by presenting problems such as -area oscillation and low frequency oscillation. It works.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. It will be appreciated.

Claims (2)

A frequency deviation Δω multiplied by a frequency feedback gain constant (1 / R) times the inverse of the speed governor speed control constant (R) is fed back (S1) by the proportional feedback gain constant K _p = 1 The proportional control is executed (S2), the integral control is executed by the integral feedback gain constant (K _I ) (S3) and the derivative control is executed by the differential feedback gain constant (K _D ) (S4) and summed to position the valve. Control input for adjustment Providing; For modeling the steam valve position limit, it is checked if the position displacement (X _GV ) of the steam valve is the maximum value (X _GV = X _GVMAX ) and -X _GV + P _c 0 (S5). If the displacement (X _GV ) is the minimum value (X _GV = X _GVMIN ) and -X _GV + P _c <0 (S6), check the steam valve position (T _H : governor time constant, P _c : position adjuster) (S7), and satisfy the conditions S5 and S6 By modeling the governor with = 0 (S8) and modeling it with a nonwindup limiter that can accurately model the mechanical structure of the valve reciprocating within the upper and lower limits, it provides a positional displacement (ΔX _GV ) of the steam valve. step; A turbine modeling step (S9) first approximated by (T _T : turbine time constant, P _m : mechanical power); Outputting a generation amount ΔP _m (MW) (S10); Providing a ΔP _m -ΔP _D by receiving a load requirement ΔP _D corresponding to the disturbance (S11); Generator kinematic equation (D: damping coefficient, P _D : disturbance) modeling a generator using a swing equation to improve the damping effect of the generator to achieve stabilization of the system (S12); And And a step (S13) of feeding back and outputting a frequency deviation [Delta] [omega] that quickly stabilizes the system. The method of claim 1, To ensure the stability of the system in the proportional differential integral (PID) frequency controller Select the differential feedback gain constant (K _D ) of the open loop transfer function to a value greater than the critical differential feedback gain constant (K _{D, crit} ) _, which is the minimum margin to ensure stability, and adjust the governor speed control constant ( governor droop) Integral feedback gain constant (K _I ) is chosen to be less than critical integral feedback gain constant (K _{I, crit} ) to ensure absolute stability to R value, which ensures the stability of the system and Governor droop) A method of improving the stabilization of the frequency control system and the damping of the generator by the modified PID control method, characterized in that the PID frequency controller increases the system damping (Damping) significantly as the R value decreases.