Transient stability margin evaluation method for network construction type power generation system

Abstract

The invention discloses a transient stability margin evaluation method for a grid-forming type power generation system. The method comprises the following steps: calculating three-phase voltage and current signals of a grid-connected point to obtain output power, and taking the output power as an input signal of a power ring; the power loop output angular frequency, the transient stability margin, the equivalent limit cut-off angle and the equivalent limit cut-off time are calculated in sequence, the actual fault detection delay is compared with the equivalent limit cut-off time, whether transient instability occurs in the fault stage of the grid-forming type power generation system or not can be judged according to the method, and the transient stability margin value is quantitatively calculated.

Description

Technical Field

[0001] The present invention relates to a transient stability margin assessment method for a grid-type power generation system, which is applicable to a grid-type power generation system under a symmetrical short-circuit fault in an AC power grid. The method can quantitatively assess the transient synchronization stability of the grid-type power generation system under a symmetrical short-circuit fault in an AC power grid during a fault stage. Background Art

[0002] With the access of large-scale power electronic power generation equipment to the power grid, the dynamic behavior and operating characteristics of traditional power systems mainly composed of synchronous generators will undergo profound changes. Under this situation, grid-connected power generation systems with the ability to actively support renewable energy have gradually become one of the current research hotspots. Grid-connected control technology enables new energy power generation systems to obtain the anti-disturbance capabilities of traditional power generation systems by simulating the transient characteristics of traditional synchronous machines. Therefore, proposing a method that can quantify the transient stability margin of grid-connected power generation systems during power grid short-circuit faults is a key issue in the current development of new energy power generation technology. At present, scholars at home and abroad have carried out a series of related studies, such as the following published literature:

[0003] [1]

[0004] [2]Z.Shuai, C.Shen,

[0005] Reference [1] studied the influence of virtual resistance on the transient stability of grid-type systems based on phase plane analysis and attraction domain, and proved that reducing the active reference power during LVRT can improve the transient stability of the system, but the reference did not quantify the transient stability margin. Reference [2] judged the transient stability of grid-type systems by approximate Lyapunov analysis method, and studied the influence of control parameters and line parameters on the operating characteristics of grid-type systems. The constructed energy function can quantitatively evaluate the transient stability margin of the system, but the method is relatively complex and the energy function lacks intuitive and fast evaluation criteria. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to propose a transient stability margin assessment method suitable for a grid-type power generation system during a fault stage. The method can determine whether a transient instability will occur in the grid-type power generation system during the fault stage, and quantitatively calculate the transient stability margin value of the grid-type power generation system.

[0007] The technical solution of the present invention is achieved in this way:

[0008] A method for evaluating transient stability margin of a grid-connected power generation system, characterized in that the specific steps are as follows:

[0009] A1) The grid-connected power generation system adopts the generator convention, by collecting the three-phase voltage signal U t And the three-phase current signal I t , calculate the output active power P and reactive power Q;

[0010] A2) Taking P and Q as the input signals of the power loop, the control equation of the grid-type power generation system is obtained as follows:

[0011]

[0012] Among them, T j and D are virtual inertia coefficient and damping coefficient respectively; ω GFM and ω0 are the virtual angular frequency of the grid-connected power generation system and the rated value of the grid angular frequency respectively; P * , P are the command value and actual value of output active power respectively; K Q is the reactive power droop coefficient; Q * , Q are the output reactive power command value and actual value respectively; U t * and U0 are the output voltage command value and the amplitude command of the virtual internal potential respectively;

[0013] A3) Based on step A2), the equivalent energy of the quantified system at different operation stages is obtained according to the control equation of the grid-type power generation system:

[0014]

[0015] Where δ is the grid connection point voltage U t The voltage at the common connection point U g The phase angle difference is the equivalent power angle; Z is the line impedance; is the line impedance angle;

[0016] A4) Based on step A3), the transient stability margin of the grid-connected power generation system during the fault phase is quantified according to the following formula:

[0017]

[0018] Among them, S acc , S dec and S D They respectively represent the equivalent acceleration area, equivalent deceleration area and equivalent damping area of ​​the grid-connected power generation system switching from the normal operation stage to the fault persistence stage; δ0 is the equivalent power angle at the initial moment of the fault detection stage, δ1 is the equivalent power angle at the initial moment of the fault persistence stage, δ max is the upper limit of the equivalent power angle during the fault continuation phase, U f is the voltage amplitude during the common connection point fault, and are the active power instructions of the grid-connected power generation system during normal period and low voltage ride-through period, S nm It is the transient stability margin assessment value of the grid-type power generation system switching from the normal operation stage to the fault continuation stage;

[0019] A5) According to step A4), the equivalent limit cut-off angle of the grid-type power generation system is calculated according to the following formula:

[0020]

[0021] A6) obtained according to step A5) The fault detection limit time of the grid-connected power generation system, i.e. the equivalent limit removal time, is calculated according to the following formula:

[0022]

[0023] Among them, ω b is the base angular frequency;

[0024] A7) The following formula is used as the transient stability criterion for the grid-connected power generation system:

[0025]

[0026] Among them, t delayis the actual fault detection delay; when the grid-connected power generation system meets the above stability criteria, it can smoothly reach and stably operate in the low voltage ride-through control mode during the fault stage.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention can quantitatively calculate the transient stability margin value of the grid-type power generation system according to the degree of power grid fault, the control characteristics and operating conditions of the grid-type power generation system and the impedance of the transmission line. It can be used for transient instability criterion and transient stability margin evaluation of the grid-type power generation system in the fault stage, and provide guiding suggestions for the large-scale development of the grid-type power generation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the control block diagram of the grid-type power generation system.

[0030] Figure 2 This is a block diagram of the active power-frequency control link of a grid-type power generation system.

[0031] Figure 3 The time domain simulation results of the grid-type power generation system when the damping coefficients of working conditions 1 and 2 are 4 and 20 respectively.

[0032] Figure 4 The active power instructions for working condition 3 and working condition 4 are P f * =0.3pu and P f * =0.2pu, time domain simulation results of the grid-connected power generation system.

[0033] Figure 5 The voltage of the common connection point during the fault of working condition 5 and working condition 6 is U f =0.15pu and U f =0.2pu, time domain simulation results of the grid-connected power generation system. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] Figure 1 This is the control block diagram of the grid-type power generation system. Figure 2 This is a block diagram of the active power-frequency control link of a grid-type power generation system.

[0036] The present invention provides a transient stability margin assessment method for a grid-type power generation system, which is used to determine the transient stability of the grid-type power generation system during a fault phase. The specific implementation steps are as follows:

[0037] A1) The grid-connected power generation system adopts the generator convention, by collecting the three-phase voltage signal U t And the three-phase current signal I t , calculate the output active power P and reactive power Q;

[0038] A2) Taking P and Q as the input signals of the power loop, the control equation of the grid-type power generation system is obtained as follows:

[0039]

[0040] Among them, T j and D are virtual inertia coefficient and damping coefficient respectively; ω GFM and ω0 are the virtual angular frequency of the grid-connected power generation system and the rated value of the grid angular frequency respectively; P * , P are the command value and actual value of output active power respectively; K Q is the reactive power droop coefficient; Q * , Q are the output reactive power command value and actual value respectively; U t * and U0 are the output voltage command value and the amplitude command of the virtual internal potential respectively;

[0041] A3) Based on step A2), the equivalent energy of the quantified system at different operation stages is obtained according to the control equation of the grid-type power generation system:

[0042]

[0043] Where δ is the grid connection point voltage U t The voltage at the common connection point U g The phase angle difference is the equivalent power angle; Z is the line impedance; is the line impedance angle;

[0044] A4) Based on step A3), the transient stability margin of the grid-connected power generation system during the fault phase is quantified according to the following formula:

[0045]

[0046] Among them, S acc , S dec and S D They respectively represent the equivalent acceleration area, equivalent deceleration area and equivalent damping area of ​​the grid-connected power generation system switching from the normal operation stage to the fault persistence stage; δ0 is the equivalent power angle at the initial moment of the fault detection stage, δ1 is the equivalent power angle at the initial moment of the fault persistence stage, δ max is the upper limit of the equivalent power angle during the fault continuation phase, U f is the voltage amplitude during the common connection point fault, and are the active power instructions of the grid-connected power generation system during normal period and low voltage ride-through period, S nm It is the transient stability margin assessment value of the grid-type power generation system switching from the normal operation stage to the fault continuation stage;

[0047] A5) According to step A4), the equivalent limit cut-off angle of the grid-type power generation system is calculated according to the following formula:

[0048]

[0049] A6) obtained according to step A5) The fault detection limit time of the grid-connected power generation system, i.e. the equivalent limit removal time, is calculated according to the following formula:

[0050]

[0051] Among them, ω b is the base angular frequency, and its actual value is 100π.

[0052] A7) The following formula is used as the transient stability criterion for the grid-connected power generation system:

[0053]

[0054] Among them, t delay is the actual fault detection delay. When the grid-connected power generation system meets the above stability criteria, it can smoothly reach and stably operate in the low voltage ride-through control mode during the fault stage.

[0055] Effect description of the present invention:

[0056] Figure 3 The time domain simulation results of the grid-type power generation system are given in the working conditions 1 and 2 of the working conditions respectively when the damping coefficient is 4 and 20. When the grid voltage level drops to 0.2pu, the calculation under the working condition 1 scenario is And t delay =50ms, that is When , the transient stability criterion of the system is not met, such as Figure 3 As shown in the working condition 1, the grid-type power generation system experiences frequency increase instability; under the working condition 2 scenario, it is calculated that Right now When the transient stability criterion of the system is met, the grid-connected power generation system can smoothly enter the low voltage ride-through mode.

[0057] Figure 4 Given an active power command and The time domain simulation results of the grid-type power generation system. When the grid voltage level drops to 0.2pu and Pf * =0.3pu, we can calculate Right now When , the transient stability criterion of the system is not met, such as Figure 4 As shown in the working condition 3, the grid-type power generation system has frequency increase instability phenomenon; in the working condition 4 Calculated Right now When the transient stability criterion of the system is met, the grid-connected power generation system can smoothly enter the low voltage ride-through mode.

[0058] Figure 5 The common connection point voltage U is given f =0.15pu and U f =0.2pu, the time domain simulation results of the grid-type power generation system. f =0.15pu, we can calculate Right now When , the transient stability criterion of the system is not met, such as Figure 5 As shown in the working condition 5, the grid-type power generation system has frequency increase instability phenomenon; in working condition 6, U f =0.2pu, calculated Right now When the transient stability criterion of the system is met, the grid-connected power generation system can smoothly enter the low voltage ride-through mode.

[0059] The present invention proposes a transient stability margin assessment method suitable for a grid-type power generation system during a fault stage. The method can determine whether a grid-type power generation system will experience transient instability during a fault stage based on the degree of grid voltage drop, controller delay, power instructions of the grid-type power generation system during the fault stage, power loop parameters, and transmission line impedance, and quantitatively calculate the transient stability margin value of the grid-type power generation system, thereby providing a quantitative assessment basis for the transient synchronous stability of the grid-type power generation system.

[0060] Finally, it should be noted that the above examples of the present invention are merely examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. Although the applicant has described the present invention in detail with reference to the preferred embodiments, for those of ordinary skill in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A transient stability margin assessment method for a grid-connected power generation system, characterized in that: The specific steps are as follows: A1) The grid-connected power generation system adopts the generator convention, by collecting the three-phase voltage signal U t And the three-phase current signal I t , calculate the output active power P and reactive power Q; A2) Taking P and Q as the input signals of the power loop, the control equation of the grid-type power generation system is obtained as follows: Among them, T j and D are the virtual inertia coefficient and damping coefficient respectively; ω GFM and ω0 are the virtual angular frequency of the grid-connected power generation system and the rated value of the grid angular frequency respectively; P * , P are the command value and actual value of output active power respectively; K Q is the reactive power droop coefficient; Q * , Q are the output reactive power command value and actual value respectively; and U0 are the output voltage command value and the amplitude command of the virtual internal potential respectively; A3) Based on step A2), the equivalent energy of the quantified system at different operation stages is obtained according to the control equation of the grid-type power generation system: Where δ is the grid connection point voltage U t The voltage at the common connection point U g The phase angle difference is the equivalent power angle; Z is the line impedance; is the line impedance angle; A4) Based on step A3), the transient stability margin of the grid-connected power generation system during the fault phase is quantified according to the following formula: Among them, S acc , S dec and S D They respectively represent the equivalent acceleration area, equivalent deceleration area and equivalent damping area of ​​the grid-connected power generation system switching from the normal operation stage to the fault persistence stage; δ0 is the equivalent power angle at the initial moment of the fault detection stage, δ1 is the equivalent power angle at the initial moment of the fault persistence stage, δ max is the upper limit of the equivalent power angle during the fault continuation phase, U f is the voltage amplitude during the common connection point fault, and are the active power instructions of the grid-connected power generation system during normal period and low voltage ride-through period, S nm It is the transient stability margin assessment value of the grid-type power generation system switching from the normal operation stage to the fault continuation stage; A5) According to step A4), the equivalent limit cut-off angle of the grid-type power generation system is calculated according to the following formula: A6) obtained according to step A5) The fault detection limit time of the grid-connected power generation system, i.e. the equivalent limit removal time, is calculated according to the following formula: Among them, ω b is the base angular frequency; A7) The following formula is used as the transient stability criterion for the grid-connected power generation system: Among them, t delay is the actual fault detection delay; when the grid-connected power generation system meets the above stability criteria, it can smoothly reach and stably operate in the low voltage ride-through control mode during the fault stage.

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