CN105429132A - Building method of motor load model - Google Patents

Abstract

The invention provides a building method of a motor load model. The method comprises the following steps: building the motor load model; carrying out accident simulating calculation on the motor load model; and determining frequency characteristic parameters of the motor load model. According to the building method of the motor load model provided by the invention, frequency parameters of various motor loads are accurately determined; and the method has great significance in improvement of the simulation precision and guarantee of the safety and the reliability of normal operation of a power grid. Torque-slip physical mechanism characteristics of motors are fully considered; the motor load model is good in convergence characteristics and high in robustness; the defect that a traditional load model cannot accurately describe load frequency characteristics of an asynchronous motor cluster is overcome; the simulating calculation reliability of a power system is improved; and a strong guarantee is provided for scientific planning and safe and stable operation of a power system.

Description

A kind of construction method of induction-motor load model

Technical field

The present invention relates to Simulating technique in Electric Power System, be specifically related to a kind of construction method of induction-motor load model.

Background technology

Along with the raising of Power System Interconnection degree, the dynamic characteristic of electrical network under fault becomes and becomes increasingly complex, in order to improve the generation of the fail safe prevention large-scale blackout of electrical network, often need to fully understand electrical network characteristic in a particular state in Electric Power Network Planning with in running.Because on the one hand the requirement of electrical network self determines and can not do experiment carry out Study system stability in actual electric network, in addition on the one hand emulation institute for the anticipation situation in running status future often, also do not occur in the middle of reality, can not study the stability of electrical network in systems in practice so also determine.Emulate in this case and just become operation of power networks, planning, the requisite instrument of design.

In the electric power system of actual motion, dynamic process of frequency curve can be obtained by actual measurement, but there is larger difference sometimes in system emulation result and practical frequency dynamic process curve.1996, point out in the failure analysis report of the coordination committee of US West (WSCC), adopt different load models to emulate, the even diametrically opposite analysis result of difference will be obtained, this people are recognized load model is on the impact of simulation calculation and importance.

When system jam causes unbalanced power, frequency can change thereupon, especially in some isolated power network or microgrid, during fault, frequency change is often larger, and the frequency characteristic of electrical network depends on frequency character of load, therefore, consider that the load model structure and parameters of frequency characteristic aligns the system frequency dynamic characteristic confirming to know microgrid or isolated power network very important.The load model that the current emulation of China's electrical network adopts and parameter be all mostly based on the eighties in last century about Failure Simulation (partial electric grid adjusts successively to some extent) determined.But along with the great change of development in science and technology and the industrial structure, network load is formed, characteristic all great variety occurs, especially along with transregional serial-parallel power grid develops, current loads model parameter simulation accuracy and exist actually relatively large deviation, cause current loads model parameter cannot accurate description load dynamic frequency characteristic.

Summary of the invention

In order to overcome above-mentioned the deficiencies in the prior art, the invention provides a kind of construction method of induction-motor load model, overcoming conventional motors load model parameters cannot the shortcoming of accurate description dynamic load frequency characteristic, improve the confidence level that electric system simulation calculates, for the planning of science activities of electric power system and safe and stable operation provide powerful guarantee.

In order to realize foregoing invention object, the present invention takes following technical scheme:

The invention provides a kind of construction method of induction-motor load model, said method comprising the steps of:

Step 1: set up induction-motor load model;

Step 2: Failure Simulation calculating is carried out to induction-motor load model;

Step 3: the frequency characteristic parameter determining induction-motor load model.

In described step 1, induction-motor load model is as follows:

$\left\{\begin{array}{c}\frac{{\mathrm{dE}}_d^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_d^{\′}+(X-X^{\′})I_q\]-{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_q^{\′}\\ \frac{{\mathrm{dE}}_q^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_q^{\′}+(X-X^{\′})I_d\]-{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_d^{\′}\\ \frac{{\mathrm{d\ω}}_r}{dt}=\frac{1}{2T_J}\[T_E-T_M\]\\ {\mathrm{A\ω}}_0^2+{\mathrm{B\ω}}_0+C=1.0\end{array}\right.---\left(1\right)$

Wherein, ω ₀represent motor initial speed, and ω ₀=1-s ₀, s ₀represent the initial slippage of rotor; E' _drepresent motor d-axis transient potential, E' _qrepresent motor quadrature axis transient potential; I _drepresent motor d shaft current, I _qrepresent induction motor q shaft current, and I _dand I _qbe expressed as:

$I_d=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_d-E_d^{\′})+X^{\′}(V_q-E_q^{\′})\]---\left(3\right)$

$I_q=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_q-E_q^{\′})-X^{\′}(V_d-E_d^{\′})\]R_s---\left(4\right)$

Wherein, V _drepresent motor direct-axis voltage, V _qrepresent motor quadrature-axis voltage, R _srepresent stator resistance, short-circuit reactance when X' represents that rotor is motionless, and x _srepresent stator leakage reactance, X _rrepresent rotor leakage reactance, X _mrepresent excitatory reactance;

X represents the reactance of rotor open circuit, and X=X _s+ X _m;

T ₀' rotor loop time constant when representing stator open circuit, and ω _brepresent synchronous angular velocity, and ω _b=2 π f _base, f _baserepresent work frequency, get 50Hz; R _rrepresent rotor resistance;

T _jrepresent inertia time constant, T _mrepresent electrical machinery torque, T _erepresent electric electromechanics magnetic torque, and T _mand T _ebe expressed as:

$T_M=({\mathrm{A\ω}}_r^2+{\mathrm{B\ω}}_r+C)T_0---\left(5\right)$

T _E＝E′ _dI _d+E′ _qI _q(6)

Wherein: ω _rfor motor actual speed, and ω _r=1-s, s are the actual slippage of rotor; A, B, C represent the machine torque coefficient of motor, T ₀represent the initial mechanical torque of motor.

Described step 2 comprises the following steps:

Step 2-1: the active power-frequency characteristic coefficient P determining load bus _f;

Step 2-2: load cell is divided into static load and dynamic load by part throttle characteristics;

Step 2-3: the active power-frequency characteristic coefficient L calculating static load _dPwith reactive power-frequency characteristic coefficient L _dQ;

Step 2-4: the operational mode determining electric power system during accident, and determine accident analog form;

Step 2-5: machine torque coefficient A, B, C of given motor;

Step 2-6: adopt power system simulation software PSD-BPA or PSD-PSASP to carry out analog computation.

In described step 2-1, determine that the active power-frequency characteristic coefficient of load bus comprises:

If P ₀represent the burden with power initial value of load bus, k is the device type number comprised in load bus, N _ithe active power of indication equipment type i accounts for the percentage of load bus active power, and i=1 ..., k; Active power-frequency characteristic coefficient the P of device type i _firepresent, so the active-power P of device type i _ibe expressed as:

P _i＝N _i×P ₀(7)

Have according to formula (7):

$P_f=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_i\×P_{fi})}{P_0}---\left(8\right)$

Wherein, P _frepresent the active power-frequency characteristic coefficient of load bus.

In described step 2-2, described dynamic load is induction-motor load, and dynamic load comprises air-conditioning, refrigerator and washing machine;

Described static load is other loads except induction-motor load, and dynamic load comprises incandescent lamp, water heater and TV.

In described step 2-3, calculate the active power-frequency characteristic coefficient L of static load _dPwith reactive power-frequency characteristic coefficient L _dQcomprise:

If N _sifor the meritorious percentage of static load in device type i, then the active-power P of static load in device type i _sifor:

P _Si＝N _i×N _Si×P ₀(9)

So the comprehensive active-power P of static load _safor the static load active power sum of each device type in induction-motor load model, that is:

$P_{Sa}=\underset{i=1}{\overset{k}{\Σ}}{P}_{Si}---\left(10\right)$

Active power-frequency characteristic coefficient the L of static load _dPwith reactive power-frequency characteristic coefficient L _dQbe expressed as:

$L_{DP}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×P_{fi})}{P_{Sa}}---\left(11\right)$

$L_{DQ}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×Q_{fi})}{P_{Sa}}---\left(12\right)$

Wherein, P _fiactive power-the frequency characteristic coefficient of indication equipment type i, Q _fireactive power-the frequency characteristic coefficient of indication equipment type i.

Described step 3 comprises the following steps:

Step 3-1: calculate power system frequency according to the frequency variation of electric power system and the active power variable quantity of load bus and change the load bus active power percent change K caused _pf, have:

$K_{pf}=\frac{\mathrm{\Δ}P}{\mathrm{\Δ}f}\×100\%---\left(13\right)$

Wherein, Δ f represents the frequency variation of electric power system, and Δ f=f ₁-f ₀, f ₁represent that POST FAULT POWER SYSTEMS frequency retrieval is to steady timing frequency, f ₀the frequency of electric power system when expression accident starts;

Δ P represents the active power variable quantity of load bus, and Δ P=P ₁-P ₀, P ₁represent the active power of POST FAULT POWER SYSTEMS frequency retrieval to load bus when stablizing;

Step 3-2: compare K _pfwith the active power-frequency characteristic coefficient P of load bus _fif, | K _pf-P _f| be greater than 0.001, then need to adjust A, B, C, return step 2-6; Otherwise show that machine torque coefficient A, B, C of given motor are the frequency parameter of induction-motor load model.

Compared with immediate prior art, technical scheme provided by the invention has following beneficial effect:

1) the stable operation characteristic of load model on large-sized connection electrified wire netting has important impact, and induction-motor load is all induction-motor load more than 60% in power system load, dynamic load characteristic after system jam is mainly derived from the comprehensive response characteristic of induction-motor load, the construction method of induction-motor load model provided by the invention accurately determines the frequency parameter of all kinds of induction-motor load, has great importance to the fail safe improving electric system simulation precision, guarantee electrical network normally runs, reliability operation;

2) the present invention is first by active power-frequency characteristic coefficient and the reactive power-frequency characteristic coefficient of static load in Component Based determination load bus, then machine torque coefficient A, B, C of the asynchronous motor of whole load bus is determined by fault fitting method, can the frequency characteristic of accurate description load of induction motor in groups;

3) the present invention has taken into full account the torque-slippage Physical Mechanism characteristic of motor, and its convergence property is good, strong robustness;

4) instant invention overcomes traditional load model cannot the shortcoming of accurate description asynchronous motor group frequency character of load, improves the confidence level that electric system simulation calculates, for the planning of science activities of electric power system and safe and stable operation provide powerful guarantee.

Accompanying drawing explanation

Fig. 1 is the construction method flow chart of induction-motor load model in the embodiment of the present invention;

Fig. 2 is west of a city 220kV transformer station geographical wiring diagram in the embodiment of the present invention;

Fig. 3 is analogue system schematic diagram in the embodiment of the present invention;

Fig. 4 is the frequency variation curve figure of system in the embodiment of the present invention;

Fig. 5 is west of a city 220kV load bus active power curves figure in the embodiment of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The invention provides a kind of construction method of induction-motor load model, as Fig. 1, said method comprising the steps of:

Step 1: set up induction-motor load model;

Step 2: Failure Simulation calculating is carried out to induction-motor load model;

Step 3: the frequency characteristic parameter determining induction-motor load model.

In described step 1, induction-motor load model is as follows:

$\left\{\begin{array}{c}\frac{{\mathrm{dE}}_d^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_d^{\′}+(X-X^{\′})I_q\]-{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_q^{\′}\\ \frac{{\mathrm{dE}}_q^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_q^{\′}+(X-X^{\′})I_d\]-{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_d^{\′}\\ \frac{{\mathrm{d\ω}}_r}{dt}=\frac{1}{2T_J}\[T_E-T_M\]\\ {\mathrm{A\ω}}_0^2+{\mathrm{B\ω}}_0+C=1.0\end{array}\right.---\left(1\right)$

Wherein, ω ₀represent motor initial speed, and ω ₀=1-s ₀, s ₀represent the initial slippage of rotor; E' _drepresent motor d-axis transient potential, E' _qrepresent motor quadrature axis transient potential; I _drepresent motor d shaft current, I _qrepresent induction motor q shaft current, and I _dand I _qbe expressed as:

$I_d=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_d-E_d^{\′})+X^{\′}(V_q-E_q^{\′})\]---\left(3\right)$

$I_q=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_q-E_q^{\′})-X^{\′}(V_d-E_d^{\′})\]R_s---\left(4\right)$

Wherein, V _drepresent motor direct-axis voltage, V _qrepresent motor quadrature-axis voltage, R _srepresent stator resistance, short-circuit reactance when X' represents that rotor is motionless, and x _srepresent stator leakage reactance, X _rrepresent rotor leakage reactance, X _mrepresent excitatory reactance;

X represents the reactance of rotor open circuit, and X=X _s+ X _m;

T ₀' rotor loop time constant when representing stator open circuit, and ω _brepresent synchronous angular velocity, and ω _b=2 π f _base, f _baserepresent work frequency, get 50Hz; R _rrepresent rotor resistance;

T _jrepresent inertia time constant, T _mrepresent electrical machinery torque, T _erepresent electric electromechanics magnetic torque, and T _mand T _ebe expressed as:

$T_M=({\mathrm{A\ω}}_r^2+{\mathrm{B\ω}}_r+C)T_0---\left(5\right)$

T _E＝E′ _dI _d+E′ _qI _q(6)

Wherein: ω _rfor motor actual speed, and ω _r=1-s, s are the actual slippage of rotor; A, B, C represent the machine torque coefficient of motor, T ₀represent the initial mechanical torque of motor.

Described step 2 comprises the following steps:

Step 2-1: the active power-frequency characteristic coefficient P determining load bus _f;

Step 2-2: load cell is divided into static load and dynamic load by part throttle characteristics;

Step 2-3: the active power-frequency characteristic coefficient L calculating static load _dPwith reactive power-frequency characteristic coefficient L _dQ;

Step 2-4: the operational mode determining electric power system during accident, and determine accident analog form;

Step 2-5: machine torque coefficient A, B, C of given motor;

Step 2-6: adopt power system simulation software PSD-BPA or PSD-PSASP to carry out analog computation.

In described step 2-1, determine that the active power-frequency characteristic coefficient of load bus comprises:

If P ₀represent the burden with power initial value of load bus, k is the device type number comprised in load bus, N _ithe active power of indication equipment type i accounts for the percentage of load bus active power, and i=1 ..., k; Active power-frequency characteristic coefficient the P of device type i _firepresent, so the active-power P of device type i _ibe expressed as:

P _i＝N _i×P ₀(7)

Have according to formula (7):

$P_f=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_i\×P_{fi})}{P_0}---\left(8\right)$

Wherein, P _frepresent the active power-frequency characteristic coefficient of load bus.

In described step 2-2, described dynamic load is induction-motor load, and dynamic load comprises air-conditioning, refrigerator and washing machine;

Described static load is other loads except induction-motor load, and dynamic load comprises incandescent lamp, water heater and TV.

In described step 2-3, calculate the active power-frequency characteristic coefficient L of static load _dPwith reactive power-frequency characteristic coefficient L _dQcomprise:

If N _sifor the meritorious percentage of static load in device type i, then the active-power P of static load in device type i _sifor:

P _Si＝N _i×N _Si×P ₀(9)

So the comprehensive active-power P of static load _safor the static load active power sum of each device type in induction-motor load model, that is:

$P_{Sa}=\underset{i=1}{\overset{k}{\Σ}}{P}_{Si}---\left(10\right)$

Active power-frequency characteristic coefficient the L of static load _dPwith reactive power-frequency characteristic coefficient L _dQbe expressed as:

$L_{DP}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×P_{fi})}{P_{Sa}}---\left(11\right)$

$L_{DQ}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×Q_{fi})}{P_{Sa}}---\left(12\right)$

Wherein, P _fiactive power-the frequency characteristic coefficient of indication equipment type i, Q _fireactive power-the frequency characteristic coefficient of indication equipment type i.

In step 2-4, during accident, the operational mode of electric power system comprises operational mode when setting up accident according to the data of automated system record, as the power flow stability calculated data of simulating for accident, calculation of tidal current should be basically identical with Observed current data result, the ruuning situation of generator excited system, governing system, power system stabilizer, PSS and other control appliance during investigation accident, and in load model, consider the static load frequency factor of load bus, set up stability Calculation data;

Accident analog form comprises according to accident record curve line, determines accident mute time and short-circuit impedance, if there occurs the machine of cutting in process of the test, fall load disturbance, then determines how to simulate these disturbances in simulations according to measured data.

Described step 3 comprises the following steps:

Step 3-1: calculate power system frequency according to the frequency variation of electric power system and the active power variable quantity of load bus and change the load bus active power percent change K caused _pf, have:

$K_{pf}=\frac{\mathrm{\Δ}P}{\mathrm{\Δ}f}\×100\%---\left(13\right)$

Wherein, Δ f represents the frequency variation of electric power system, and Δ f=f ₁-f ₀, f ₁represent that POST FAULT POWER SYSTEMS frequency retrieval is to steady timing frequency, f ₀the frequency of electric power system when expression accident starts;

Δ P represents the active power variable quantity of load bus, and Δ P=P ₁-P ₀, P ₁represent the active power of POST FAULT POWER SYSTEMS frequency retrieval to load bus when stablizing;

Step 3-2: compare K _pfwith the active power-frequency characteristic coefficient P of load bus _fif, | K _pf-P _f| be greater than 0.001, then need to adjust A, B, C, return step 2-6; Otherwise show that machine torque coefficient A, B, C of given motor are the frequency parameter of induction-motor load model.

Embodiment

By carrying out probe to Wenzhou District of Zhejiang Province west of a city 220kV transformer station (winding diagram as shown in Figure 2), and statistical analysis calculating is carried out to the survey data at this station, when can determine large load method, to relate to the ratio that device type and each device type occupy as shown in table 1 220kV substation, the west of a city:

Table 1

Sequence number	Load type	This load type proportion (%)
			1	The large motor of industry	42.31
2	Industry small size motor	1.21
			3	Fluorescent lamp	12.84
4	Sodium vapor lamp	4.4
			5	Refrigeration-type air-conditioning	5.44
6	Water heater	7.72
			7	Colour TV	7.01
8	Refrigerator	3.99
			9	Washing machine	3.49
10	Electromagnetic oven	2.07
			11	Electric furnace	6.88
12	Computer	2.64

According to the load detailed statistics of west of a city 220kV transformer station, COMPREHENSIVE CALCULATING is carried out to the load in above-mentioned all devices type, the meritorious frequency factor P of west of a city varying duty can be obtained _fbe 3.3%, the machine torque coefficient that the west of a city becomes asynchronous motor group is respectively: A is 0.31 into 0.69, B is 0, C.Finally can obtain the west of a city and become the integrated load model (SLM) of consideration distribution network as table 2:

Table 2

Wherein, Tj represents motor inertia time constant, Rs represents motor stator resistance, Xs represents motor stator reactance, Xm represents the excitatory reactance of motor, Rr represents motor rotor resistance, Xr represents motor rotor reactance, R* represents distribution branch resistance, X* represents the reactance of distribution branch road, ZP% represents the constant-impedance composition in static burden with power formation, ZQ% represents the constant-impedance composition in static reactive load structure, IP% represents the constant current composition in static burden with power formation, IQ% represents the constant current composition in static reactive load structure, PP% represents the invariable power composition in static burden with power formation, PQ% represents the anti-composition of invariable power in static reactive load structure.As follows.Motor load rate is 40%.

For verifying the validity of the construction method of induction-motor load model proposed by the invention, (system of 110kV, 35kV distribution network in varying duty district, Hancheng, reactive power compensation and 110kV, 35kV, 10kV, 6kV load bus is comprised with the load model parameters of the current employing of west of a city 220kV transformer station, the load model parameters adopting this method to generate and original system, as shown in Figure 2) carry out simulation comparison, the validity of the construction method of the induction-motor load model that authentication is proposed by the invention.

As Fig. 3, a generating set is powered to west of a city change and Bus4 by double-circuit line, and the burden with power that the burden with power that the west of a city becomes is 167MW, Bus4 is 40MW.

Simulated conditions: when analogue system runs 0.1 second, Bus4 node increases 40MW burden with power.

Respectively the west of a city 220kV transformer station 110kV shown in Fig. 2 and following system thereof, the existing load model of equivalent SLM model and East China are connected on the load bus shown in Fig. 3 and emulate, obtain the frequency variation curve of system and west of a city 220kV load bus active power curves as shown in Figure 4 and Figure 5.Comparative analysis frequency variation curve and active power curves, can see that the fitting effect of the simulation curve adopting SLM model and detailed system is significantly better than adopting existing load model parameters.Therefore compared with current load model parameters, adopt this method can describe motor frequency characteristic better, the system action of the system performance more approaching to reality during fault post-simulation is calculated, improve the confidence level of Simulation Analysis, for electric power system work out the operation of science, control program provides guarantee.

Finally should be noted that: above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit; those of ordinary skill in the field still can modify to the specific embodiment of the present invention with reference to above-described embodiment or equivalent replacement; these do not depart from any amendment of spirit and scope of the invention or equivalent replacement, are all applying within the claims of the present invention awaited the reply.

Claims (7)

1. a construction method for induction-motor load model, is characterized in that: said method comprising the steps of:

Step 1: set up induction-motor load model;

Step 2: Failure Simulation calculating is carried out to induction-motor load model;

Step 3: the frequency characteristic parameter determining induction-motor load model.

2. the construction method of induction-motor load model according to claim 1, it is characterized in that: in described step 1, induction-motor load model is as follows:

$\left\{\begin{array}{c}\frac{{\mathrm{dE}}_d^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_d^{\′}+(X-X^{\′})I_q\]-{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_q^{\′}\\ \frac{{\mathrm{dE}}_q^{\′}}{dt}=-\frac{1}{T_0^{\′}}\[E_q^{\′}-(X-X^{\′})I_d)+{\mathrm{\ω}}_b({\mathrm{\ω}}_r-1)E_d^{\′}\\ \frac{{\mathrm{d\ω}}_r}{dt}=\frac{1}{2T_J}\[T_E-T_M\]\\ {\mathrm{A\ω}}_0^2+{\mathrm{B\ω}}_0+C=1.0\end{array}\right.---\left(1\right)$

Wherein, ω ₀represent motor initial speed, and ω ₀=1-s ₀, s ₀represent the initial slippage of rotor; E' _drepresent motor d-axis transient potential, E' _qrepresent motor quadrature axis transient potential; I _drepresent motor d shaft current, I _qrepresent induction motor q shaft current, and I _dand I _qbe expressed as:

$I_d=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_d-E_d^{\′})+X^{\′}(V_q-E_q^{\′})\]---\left(3\right)$

$I_q=\frac{1}{R_s^2+X^{\′2}}\[R_s(V_q-E_q^{\′})-X^{\′}(V_d-E_d^{\′})\]R_s---\left(4\right)$

Wherein, V _drepresent motor direct-axis voltage, V _qrepresent motor quadrature-axis voltage, R _srepresent stator resistance, short-circuit reactance when X' represents that rotor is motionless, and x _srepresent stator leakage reactance, X _rrepresent rotor leakage reactance, X _mrepresent excitatory reactance;

X represents the reactance of rotor open circuit, and X=X _s+ X _m;

T ' ₀rotor loop time constant when representing that stator is opened a way, and ω _brepresent synchronous angular velocity, and ω _b=2 π f _base, f _baserepresent work frequency, get 50Hz; R _rrepresent rotor resistance;

T _jrepresent inertia time constant, T _mrepresent electrical machinery torque, T _erepresent electric electromechanics magnetic torque, and T _mand T _ebe expressed as:

$T_M=({\mathrm{A\ω}}_r^2+{\mathrm{B\ω}}_r+C)T_0---\left(5\right)$

T _E＝E′ _dI _d+E′ _qI _q(6)

Wherein: ω _rfor motor actual speed, and ω _r=1-s, s are the actual slippage of rotor; A, B, C represent the machine torque coefficient of motor, T ₀represent the initial mechanical torque of motor.

3. the construction method of induction-motor load model according to claim 2, is characterized in that: described step 2 comprises the following steps:

Step 2-1: the active power-frequency characteristic coefficient P determining load bus _f;

Step 2-2: load cell is divided into static load and dynamic load by part throttle characteristics;

Step 2-3: the active power-frequency characteristic coefficient L calculating static load _dPwith reactive power-frequency characteristic coefficient L _dQ;

Step 2-4: the operational mode determining electric power system during accident, and determine accident analog form;

Step 2-5: machine torque coefficient A, B, C of given motor;

Step 2-6: adopt power system simulation software PSD-BPA or PSD-PSASP to carry out analog computation.

4. the construction method of induction-motor load model according to claim 3, is characterized in that: in described step 2-1, determines that the active power-frequency characteristic coefficient of load bus comprises:

If P ₀represent the burden with power initial value of load bus, k is the device type number comprised in load bus, N _ithe active power of indication equipment type i accounts for the percentage of load bus active power, and i=1 ..., k; Active power-frequency characteristic coefficient the P of device type i _firepresent, so the active-power P of device type i _ibe expressed as:

P _i＝N _i×P ₀(7)

Have according to formula (7):

$P_f=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_i\×P_{fi})}{P_0}---\left(8\right)$

Wherein, P _frepresent the active power-frequency characteristic coefficient of load bus.

5. the construction method of induction-motor load model according to claim 3, is characterized in that: in described step 2-2, described dynamic load is induction-motor load, and dynamic load comprises air-conditioning, refrigerator and washing machine;

Described static load is other loads except induction-motor load, and dynamic load comprises incandescent lamp, water heater and TV.

6. the construction method of induction-motor load model according to claim 4, is characterized in that: in described step 2-3, calculates the active power-frequency characteristic coefficient L of static load _dPwith reactive power-frequency characteristic coefficient L _dQcomprise:

If N _sifor the meritorious percentage of static load in device type i, then the active-power P of static load in device type i _sifor:

P _Si＝N _i×N _Si×P ₀(9)

So the comprehensive active-power P of static load _safor the static load active power sum of each device type in induction-motor load model, that is:

$P_{Sa}=\underset{i=1}{\overset{k}{\Σ}}{P}_{Si}---\left(10\right)$

Active power-frequency characteristic coefficient the L of static load _dPwith reactive power-frequency characteristic coefficient L _dQbe expressed as:

$L_{DP}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×P_{fi})}{P_{Sa}}---\left(11\right)$

$L_{DQ}=\frac{\underset{i=1}{\overset{k}{\Σ}}(P_{Si}\×Q_{fi})}{P_{Sa}}---\left(12\right)$

Wherein, P _fiactive power-the frequency characteristic coefficient of indication equipment type i, Q _fireactive power-the frequency characteristic coefficient of indication equipment type i.

7. the construction method of induction-motor load model according to claim 1, is characterized in that: described step 3 comprises the following steps:

Step 3-1: calculate power system frequency according to the frequency variation of electric power system and the active power variable quantity of load bus and change the load bus active power percent change K caused _pf, have:

$K_{pf}=\frac{\mathrm{\Δ}P}{\mathrm{\Δ}f}\×100\%---\left(13\right)$

Wherein, Δ f represents the frequency variation of electric power system, and Δ f=f ₁-f ₀, f ₁represent that POST FAULT POWER SYSTEMS frequency retrieval is to steady timing frequency, f ₀the frequency of electric power system when expression accident starts;

Δ P represents the active power variable quantity of load bus, and Δ P=P ₁-P ₀, P ₁represent the active power of POST FAULT POWER SYSTEMS frequency retrieval to load bus when stablizing;

Step 3-2: compare K _pfwith the active power-frequency characteristic coefficient P of load bus _fif, | K _pf-P _f| be greater than 0.001, then need to adjust A, B, C, return step 2-6; Otherwise show that machine torque coefficient A, B, C of given motor are the frequency parameter of induction-motor load model.