CN104734160A - Electric power system under frequency load shedding method based on load energy - Google Patents

Abstract

The invention relates to an electric power system under frequency load shedding method based on load energy. The electric power system under frequency load shedding method based on load energy is characterized by comprising the step of vacancy estimation of load energy and system power and the step of load shedding distribution based on unit load energy. The method effectiveness for determining an electric power system under frequency load shedding scheme based on load energy can be fully reflected, and high practical application value is achieved.

Description

Based on the electric power system low frequency deloading method of load and energy

Technical field

The present invention is a kind of electric power system low frequency deloading method based on load and energy, is applied to the correlation analysis of power system load Study of Transient Energy, load and energy and frequency, the formulation of UFLS control strategy etc.

Background technology

Electric power system is an energy system, and energy keeps constant under steady state conditions.But when system suffers large disturbances, system will have a large amount of transient state energies to inject, after disturbance terminates, system total terpene lactones.Study system is cutting the load and energy regularity of distribution under machine disturbance, from the method for energy point of view research frequency dynamic problem and UFLS solution formulation.

Summary of the invention

The object of this invention is to provide a kind of from energy point of view research frequency dynamic problem and UFLS, strong adaptability, has the electric power system low frequency deloading method based on load and energy of higher actual application value.

The object of the invention is to be realized by following technical scheme: a kind of electric power system low frequency deloading method based on load and energy, it is characterized in that, it comprises following content:

1) load and energy

The transient potential energy of load D is

$V_{P_D}\left(t\right)={\∫}_{t_0}^t{\mathrm{\ω}}_N[P_D\left(u\right)-P_D^s]\mathrm{\ω}\left(u\right)\mathrm{du}---\left(1\right)$

Wherein: for the transient potential energy of t load D,

ω _nfor system nominal angular frequency,

P _du () is the active power of u moment load D,

for corresponding to the active power of system stability balance point before load D fault,

ω (u) is the angular frequency of u moment load bus,

for u is at moment t ₀to the definite integral of t,

U is integration variable;

Specific load energy is

$V_{U_{\mathrm{PD}}}=V_{P_D}/S_u---\left(2\right)$

Wherein: for unit load and energy,

for load and energy,

S _ufor load apparent power;

Specific load energy changing slope is

$k_{U_{\mathrm{PD}}}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\frac{V_{U_{\mathrm{PD}}}\left(t_{i+1}\right)-V_{U_{\mathrm{PD}}}\left(t_i\right)}{\mathrm{\Δt}}\right)/n---\left(3\right)$

Wherein: for unit load and energy change slope,

for t _imoment specific load energy,

for t _i+1moment specific load energy,

Δ t is t _iwith t _i+1the time interval,

for i is from 1 to n summation symbol,

N is time span;

2) system power vacancy is estimated

System frequency difference rate of change characterizes the seriousness that system has an accident, and estimating system power shortage amount expression formula is more accurately

$\frac{\mathrm{d\Δf}}{\mathrm{dt}}{|}_{t=0}=-\frac{\mathrm{\Δ}{P}_L}{2H}---\left(4\right)$

Wherein: Δ P _lfor the variable quantity of load after system generation disturbance,

for disturbance initial time system frequency difference rate of change,

H is system equivalent moment of inertia;

System equivalent moment of inertia is

$H=\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{H}_i\·S_i}{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{S}_i}---\left(5\right)$

Wherein: H is system equivalent moment of inertia,

H _ibe the moment of inertia of i-th generator,

S _ibe the apparent power of i-th generator,

for i is from 1 to n summation symbol,

N is the number of units of generator;

3) off-load based on specific load energy distributes

The first step: to calculate in actual path specific load energy changing slope between age at failure and sort;

Second step: find maximum position, specific load energy slope value gap as cutting load line of demarcation;

3rd step: preferentially excise the larger a group load of specific load energy according to specific load energy order from large to small.

Utilize method of the present invention to determine the electric power system UFLS scheme based on load and energy, fully react the validity that the method is determined the electric power system UFLS scheme based on load and energy, there is higher actual application value.

Accompanying drawing explanation

Fig. 1 is NEW ENGLAND 10 machine 39 node system wiring schematic diagram;

Fig. 2 is system each LOAD FREQUENCY change schematic diagram;

Fig. 3 system unit load and energy change schematic diagram;

Fig. 4 is system unit load and energy change slope schematic diagram;

Fig. 5 is the off-load scheme comparison schematic diagram by energy distribution off-load amount and each load mean allocation off-load amount.

Embodiment

Electric power system low frequency deloading method based on load and energy of the present invention, comprises following content:

1) load and energy

The transient potential energy of load D is

$V_{P_D}\left(t\right)={\∫}_{t_0}^t{\mathrm{\ω}}_N[P_D\left(u\right)-P_D^s]\mathrm{\ω}\left(u\right)\mathrm{du}---\left(1\right)$

Wherein: for the transient potential energy of t load D,

ω _nfor system nominal angular frequency,

P _du () is the active power of u moment load D,

for corresponding to the active power of system stability balance point before load D fault,

ω (u) is the angular frequency of u moment load bus,

for u is at moment t ₀to the definite integral of t,

U is integration variable;

Specific load energy is

$V_{U_{\mathrm{PD}}}=V_{P_D}/S_u---\left(2\right)$

Wherein: for unit load and energy,

for load and energy,

S _ufor load apparent power;

Specific load energy changing slope is

$k_{U_{\mathrm{PD}}}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\frac{V_{U_{\mathrm{PD}}}\left(t_{i+1}\right)-V_{U_{\mathrm{PD}}}\left(t_i\right)}{\mathrm{\Δt}}\right)/n---\left(3\right)$

Wherein: for unit load and energy change slope,

for t _imoment specific load energy,

for t _i+1moment specific load energy,

Δ t is t _iwith t _i+1the time interval,

for i is from 1 to n summation symbol,

N is time span;

2) system power vacancy is estimated

System frequency difference rate of change characterizes the seriousness that system has an accident, and estimating system power shortage amount expression formula is more accurately

$\frac{\mathrm{d\Δf}}{\mathrm{dt}}{|}_{t=0}=-\frac{\mathrm{\Δ}{P}_L}{2H}---\left(4\right)$

Wherein: Δ P _lfor the variable quantity of load after system generation disturbance,

for disturbance initial time system frequency difference rate of change,

H is system equivalent moment of inertia;

System equivalent moment of inertia is

$H=\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{H}_i\·S_i}{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{S}_i}---\left(5\right)$

Wherein: H is system equivalent moment of inertia,

H _ibe the moment of inertia of i-th generator,

S _ibe the apparent power of i-th generator,

for i is from 1 to n summation symbol,

N is the number of units of generator;

3) off-load based on specific load energy distributes

The first step: to calculate in actual path specific load energy changing slope between age at failure and sort;

Second step: find maximum position, specific load energy slope value gap as cutting load line of demarcation;

3rd step: preferentially excise the larger a group load of specific load energy according to specific load energy order from large to small.

Instantiation:

With NEW ENGLAND 10 machine 39 node system for example basis, its system wiring as shown in Figure 1.Under given trend mode, arrange 38 node generators and excise when 0s, first carry out the estimation of system vacancy, can obtain system power vacancy is 851.35MW.As shown in Figure 2, as shown in Figure 3, specific load energy changing slope as shown in Figure 4 for the change of system unit load and energy for each LOAD FREQUENCY change of system.As shown in Figure 4, the specific load energy of 21 node loads is maximum, and the specific load energy of 12 node loads is minimum.Should preferentially excise load 12, then by the size of specific load energy changing slope, off-load distribution be carried out to all the other loads, low frequency load shedding equipment is set in 49.2s time delay 0.1s action.Concrete off-load distribution sees the following form:

By the off-load scheme comparison by energy distribution off-load amount and each load mean allocation off-load amount as shown in Figure 5.As seen from Figure 5, the 851.35MW load of excision equivalent, the system inertia centre frequency recovery effects of carrying out off-load distribution by specific load energy is obviously better than the system inertia centre frequency recovery effects of mean allocation off-load amount, and both are stable at 49.7385MW and 49.0241MW respectively.Show through simulating, verifying, the electric power system low frequency deloading method based on load and energy is effective and practicality.

Claims (1)

1. based on an electric power system low frequency deloading method for load and energy, it is characterized in that, it comprises following content:

1) load and energy

The transient potential energy of load D is

$V_{P_D}\left(t\right)={\∫}_{t_0}^t{\mathrm{\ω}}_N[P_D\left(u\right)-P_D^s]\mathrm{\ω}\left(u\right)\mathrm{du}---\left(1\right)$

Wherein: for the transient potential energy of t load D,

ω _nfor system nominal angular frequency,

P _du () is the active power of u moment load D,

for corresponding to the active power of system stability balance point before load D fault,

ω (u) is the angular frequency of u moment load bus,

du is that u is at moment t ₀to the definite integral of t,

U is integration variable;

Specific load energy is

$V_{U_{\mathrm{PD}}}=V_{P_D}/S_u---\left(2\right)$

Wherein: for unit load and energy,

for load and energy,

S _ufor load apparent power;

Specific load energy changing slope is

$k_{U_{\mathrm{PD}}}=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left(\frac{V_{U_{\mathrm{PD}}}\left(t_{i+1}\right)-V_{U_{\mathrm{PD}}}\left(t_i\right)}{\mathrm{\Δt}}\right)/n---\left(3\right)$

Wherein: for unit load and energy change slope,

for t _imoment specific load energy,

for t _i+1moment specific load energy,

Δ t is t _iwith t _i+1the time interval,

for i is from 1 to n summation symbol,

N is time span;

2) system power vacancy is estimated

System frequency difference rate of change characterizes the seriousness that system has an accident, and estimating system power shortage amount expression formula is more accurately

$\frac{\mathrm{d\Δf}}{\mathrm{dt}}|t=0=-\frac{\mathrm{\Δ}{P}_L}{2H}---\left(4\right)$

Wherein: Δ P _lfor the variable quantity of load after system generation disturbance,

for disturbance initial time system frequency difference rate of change,

H is system equivalent moment of inertia;

System equivalent moment of inertia is

$H=\frac{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{H}_i\·S_i}{\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{S}_i}---\left(5\right)$

Wherein: H is system equivalent moment of inertia,

H _ibe the moment of inertia of i-th generator,

S _ibe the apparent power of i-th generator,

for i is from 1 to n summation symbol,

N is the number of units of generator;

3) off-load based on specific load energy distributes

The first step: to calculate in actual path specific load energy changing slope between age at failure and sort;

Second step: find maximum position, specific load energy slope value gap as cutting load line of demarcation;

3rd step: preferentially excise the larger a group load of specific load energy according to specific load energy order from large to small.