Transient stability analysis method, device and system for new energy power system

Abstract

The invention discloses a transient stability analysis method, device and system for a new energy power system, and belongs to the technical field of new energy power generation, and the method comprises the steps: setting a network-type converter of the new energy power system as a voltage source in a normal state, and switching the network-type converter into a current source in a fault state; and representing a first transient analysis model corresponding to the grid-forming converter and a second transient analysis model corresponding to the grid-forming converter by using a curved surface, thereby determining respective power angle stable regions of the two converters, analyzing actual power angles of the new energy power system when different power grid voltages drop, observing power angle swing tracks of the converters, and calculating the power angle stability of the new energy power system. And therefore, transient weak converters corresponding to different power grid voltage sags can be accurately reflected. Compared with the prior art, the method can accurately describe the power angle stable areas of the grid-forming converters, simulates the new energy power system under various fault conditions, provides a powerful basis for preventing system instability in advance, and improves the operation reliability of the new energy power system.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation, and more specifically, relates to a transient stability analysis method, device and system for a renewable energy power system. Background Art

[0002] Against the backdrop of a global push for clean energy development, the penetration of renewable energy into power systems is rapidly increasing. In this process, grid-following converters, owing to their crucial role in integrating renewable energy into the grid, have become widely used. However, their reliance on phase-locked loops (PLLs) presents significant limitations in weak grid environments. In contrast, grid-forming converters actively support the grid, enhancing its stability by establishing stable frequency and voltage. However, when grid-following converters and grid-forming converters operate in parallel, the dynamic coupling between them is complex. This coupling can lead to power angle divergence, destabilizing the system.

[0003] Currently, there are numerous deficiencies in addressing the transient power angle stability of converters. Existing research primarily focuses on single-converter systems, failing to fully consider the coupling characteristics of grid-following and grid-forming converters in parallel. Accurate coupling modeling methods for parallel systems are lacking. Furthermore, effective quantitative methods for assessing system stability margins are lacking, making it difficult to accurately determine system stability.

[0004] Therefore, in order to ensure the reliable operation of the new energy power system, a systematic method is urgently needed that can comprehensively consider the coupling effect, accurately define the stability boundary and realize optimized control, so as to solve the transient stability problem when the grid converter is operated in parallel and promote the efficient application of new energy in the power field. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the existing technology, the present invention provides a transient stability analysis method, device and system for a new energy power system, the purpose of which is to solve the technical problem that the transient stability of the existing new energy power system is difficult to accurately evaluate.

[0006] To achieve the above objectives, according to one aspect of the present invention, a transient stability analysis method for a new energy power system is provided. The new energy power system is a parallel system consisting of a grid-forming converter and a grid-following converter, each connected to a common coupling point via respective lines and corresponding filters, and then connected to the grid via grid impedance. The transient stability analysis method comprises:

[0007] S1: setting the grid-connected converter of the new energy power system to be a current source in both normal and fault states; setting the grid-connected converter of the new energy power system to be a voltage source in the normal state and to be a current source in the fault state;

[0008] S2: constructing a first transient analysis model corresponding to the grid-forming converter represented by a curved surface and a second transient analysis model corresponding to the grid-following converter represented by a curved surface using the circuit equation of the new energy power system;

[0009] S3: using the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as the power angle stable regions of their respective converters;

[0010] S4: Analyze the actual power angle of the new energy power system when different grid voltage drops occur; if the actual power angle exceeds the power angle stability region corresponding to the grid-forming converter, it is regarded as the grid-forming converter being unstable; if the actual power angle exceeds the power angle stability region corresponding to the grid-following converter, it is regarded as the grid-following converter being unstable, thereby determining the transient weak converter corresponding to the different grid voltage drops.

[0011] Furthermore, the setting in S1 that the grid-type converter of the new energy power system is a current source in the normal state and the fault state includes: setting the control reference current of the grid-type converter in the normal state and the fault state to:

[0012] Among them, i dLref is the d-axis control reference current of the grid-following converter, i qLref is the q-axis control reference current of the grid-following converter, I NL is the rated current of the grid-following converter, θ IL is the angle of the control current of the grid-following converter relative to the d-axis.

[0013] Furthermore, the process of constructing the first transient analysis model corresponding to the grid-type converter in S2 includes: taking the power angle δ of the grid-type converter as an example, L The power angle δ of the grid-connected converter M As the horizontal and vertical axes, the q-axis voltage of the grid-following converter is taken as the z-axis, and a first transient analysis model corresponding to the grid-following converter in the new energy power system is constructed.

[0014] Furthermore, the process of determining the power angle stability region corresponding to the grid-type converter is as follows: the q-axis voltage expression v of the grid-type converter is converted into qL The part A that is not related to the power angle refLAs the reference plane; the q-axis voltage expression v of the grid-type converter qL Part A related to the power angle L With the reference plane A refL The intersection line of is used as the power angle stable area corresponding to the grid-type converter; wherein, v qL Decomposed into two parts A refL and A L , I L is the output current amplitude of the grid-following converter, Z g is the grid impedance, θ g is the impedance angle of the grid-connected impedance, Z1 is the line impedance of the grid-connected converter connected to the common coupling point, θ1 is the impedance angle of the line impedance, V g is the grid voltage amplitude, I M is the output current amplitude of the grid-type converter, θ IM is the angle of the current of the grid-type converter relative to the d-axis.

[0015] Furthermore, the normal state is set as The control reference current of the grid-type converter is: in, is the control current amplitude of the grid-type converter, I Mlim is the set current limit value, Indicates the normal state, i dMref is the d-axis control reference current of the grid-type converter, i qMref is the q-axis control reference current of the grid-type converter, Indicates the q-axis current reference value output by the voltage loop, Indicates the q-axis current reference value output by the voltage loop.

[0016] Furthermore, the fault state is set in S1 as The control reference current of the grid-type converter is: dMref ,i qMref )=(i dMF ,i qMF );in, Indicates the fault state, the grid-type converter carries the d-axis current setting value i in the fault state dMF =

[0017] I Mlim cos(θ IM ), the grid-type converter carries the q-axis current setting value i under the fault state qMF =I Mlim sin(θ IM ),θIM is the angle of the current of the grid-type converter relative to the d-axis.

[0018] Furthermore, the process of constructing the second transient analysis model corresponding to the grid-type converter in S2 includes: taking the power angle δ of the grid-type converter as an example, L The power angle δ of the grid-connected converter M The horizontal axis and vertical axis are the active power P of the grid-type converter. M The z-axis is used to construct a second transient analysis model corresponding to the grid-connected converter in the new energy power system.

[0019] Furthermore, the process of determining the power angle stable region corresponding to the grid-type converter is as follows: the active power P of the grid-type converter is M The intersection line with the reference plane corresponding to the power setting value is used as the power angle stable region corresponding to the grid-type converter.

[0020] According to another aspect of the present invention, a transient stability analysis device for a new energy power system is provided. The new energy power system is a parallel system consisting of a grid-connecting converter and a grid-following converter, each connected to a common coupling point via respective lines and corresponding filters, and then connected to the grid via grid impedance. The transient stability analysis device comprises:

[0021] A setting module is used to set the grid-following converter of the new energy power system to be a current source in both a normal state and a fault state; set the grid-forming converter of the new energy power system to be a voltage source in the normal state and to be switched to a current source in the fault state;

[0022] A characterization module, configured to construct a first transient analysis model corresponding to the grid-forming converter represented by a curved surface and a second transient analysis model corresponding to the grid-following converter represented by a curved surface using a circuit equation of the new energy power system;

[0023] a determination module, configured to use the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as power angle stability regions of their respective converters;

[0024] An analysis module is used to analyze the actual power angle of the new energy power system when different grid voltage drops occur; if the actual power angle exceeds the power angle stability region corresponding to the grid-forming converter, it is considered that the grid-forming converter is unstable; if the actual power angle exceeds the power angle stability region corresponding to the grid-following converter, it is considered that the grid-following converter is unstable, thereby determining the transient weak converter corresponding to the different grid voltage drops.

[0025] According to another aspect of the present invention, a transient stability analysis system for a new energy power system is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the transient stability analysis method when executing the computer program.

[0026] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0027] (1) The present invention provides a transient stability analysis method for a new energy power system, which sets the grid-type converter of the new energy power system as a current source in both normal and fault states; sets the grid-type converter of the new energy power system as a voltage source in the normal state and switches to a current source in the fault state; and uses a surface to represent a first transient analysis model corresponding to the grid-type converter and a second transient analysis model corresponding to the grid-type converter, thereby determining the respective power angle stability regions of the two converters, analyzing the actual power angle of the new energy power system when different grid voltages drop, observing the power angle swing trajectory of each converter, thereby accurately reflecting the transient weak converter corresponding to the different grid voltage drops. Compared with the existing stability analysis method, the present application can accurately characterize the respective power angle stability regions of the grid-type converter, simulate the new energy power system under various fault conditions, provide a strong basis for preventing system instability in advance, and improve the reliability of power system operation.

[0028] (2) This solution sets the control reference current of the grid-following converter in the normal state and the fault state as: It is considered to control the d-axis and q-axis currents of the grid-type converter through the current angle. Compared with the existing technology, it can control the q-axis current during the fault period, output reactive power, and achieve voltage support during the fault period.

[0029] (3) This solution uses the power angle δ of the grid-following converter L The power angle δ of the grid-connected converter M The first transient analysis model is constructed with the q-axis voltage of the grid-connected converter as the horizontal and vertical axes, and the q-axis voltage of the grid-connected converter as the z-axis. This model considers the influence of the grid-connected converter coupling and improves the accuracy of the modeling compared to existing technologies, achieving greater universality of the analysis conclusions.

[0030] (4) This scheme will follow the q-axis voltage expression v of the grid-type converter qL Part A related to the power angle L With the reference plane A refL The intersection line is used as the power angle stable region corresponding to the grid-type converter; the parts related to and unrelated to the power angle in the expression are taken into account. Compared with the existing technology, it can separate the expression and simplify the analysis process.

[0031] (5) This solution sets the normal state as The control reference current of the grid-type converter is: The fault current limiting of the grid-type converter is taken into consideration. Compared with the existing technology, it can ensure that the current of the grid-type converter does not exceed the set value, thereby realizing the protection of the converter device.

[0032] (6) This solution sets the fault state as The control reference current of the grid-type converter is: dMref ,i qMref )=(i dMF ,i qMF ); Considering the control of the d-axis and q-axis currents of the grid-type converter through the current angle, compared with the existing technology, it can improve the transient stability of the grid-type converter by reasonably adjusting the current angle, thereby achieving an improvement in the system stability margin.

[0033] (7) This scheme uses the power angle δ of the grid-following converter L The power angle δ of the grid-connected converter M The horizontal axis and vertical axis are the active power P of the grid-type converter. M For the z-axis, a second transient analysis model is constructed; the influence of coupling with the grid-type converter is taken into account. Compared with the existing technology, it can improve the accuracy of modeling and achieve an improvement in the universality of the analysis conclusions.

[0034] (8) This solution converts the active power P of the grid-type converter into M The intersection line with the reference plane corresponding to the power setting value is used as the power angle stable region corresponding to the grid-type converter; the influence of the current limiting of the grid-type converter on the shape of the active power surface is taken into account. Compared with the existing technology, it can accurately quantify the power angle boundary of the grid-type converter and provide guidance for the analysis of the transient stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is the topology diagram of the new energy power system in Example 1 of the present invention;

[0036] Figure 2 is a flow chart of a transient stability analysis method for a new energy power system in Example 1 of the present invention;

[0037] Figure 3 This is a control block diagram of a grid-following converter and a grid-forming converter in Example 1 of the present invention;

[0038] Figure 4 1 is an equivalent circuit and power angle curve diagram of a single-machine grid-type converter in Example 1 of the present invention;

[0039] Figure 5 1 is an equivalent circuit and power angle curve diagram of a single-mechanism grid-type converter in Example 1 of the present invention;

[0040] Figure 6 is a phasor diagram under current limiting conditions of the new energy power system in Example 1 of the present invention;

[0041] Figure 7 A in Example 1 of the present invention L and P M Surface plot;

[0042] Figure 8 Schematic diagram of the power angle stability region of the new energy power system in Example 1 of the present invention;

[0043] Figure 9 This is a power angle trajectory diagram of critical stable removal of the new energy power system under different faults in Example 1 of the present invention;

[0044] Figure 10 is the maximum deceleration volume DV in Example 1 of the present invention L and DV M Schematic diagram of . DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0046] Example 1

[0047] The present invention provides a transient stability analysis method for a new energy power system, wherein the new energy power system is a parallel system consisting of a grid-following converter and a grid-forming converter which are connected to a common coupling point through their respective lines and corresponding filters and then connected to the grid through the grid impedance. Figure 1 As shown, the grid-type converter includes L f1 and C f1 LC filter, and then connected to the common coupling point PCC through the line impedance Z1; the grid-type converter is connected to the common coupling point PCC through the line impedance Z1; f2 and C f2 The LC filter is then connected to the PCC via the line impedance Z2.

[0048] Further, such as Figure 2As shown, the transient stability analysis method includes the following steps. S1: Assume that the grid-type converter of the parallel system is a current source in both normal and fault states; Assume that the grid-type converter of the parallel system is a voltage source in normal state and switches to a current source in fault state; S2: Use the circuit equation of the parallel system to construct a first transient analysis model corresponding to the grid-type converter represented by a surface and a second transient analysis model corresponding to the grid-type converter represented by a surface; S3: The intersection of the first transient analysis model and the second transient analysis model with their respective reference planes is used as the power angle stability region of each converter; S4: Analyze the actual power angle of the parallel system under different grid voltage drops; If the actual power angle exceeds the power angle stability region corresponding to the grid-type converter, it is considered that the grid-type converter is unstable; If the actual power angle exceeds the power angle stability region corresponding to the grid-type converter, it is considered that the grid-type converter is unstable, thereby determining the transient weak converter corresponding to different grid voltage drops.

[0049] Specifically, for a parallel system corresponding to a grid-type converter and a grid-type converter, when a fault occurs, the grid-type converter can be equivalent to a current with a current amplitude and phase of I M and (δ M +θ IM ) current source, the grid-type converter is equivalent to a current with amplitude and phase I L and (δ L +θ IL ) current source, the circuit equation can be further written based on this, and the voltage of PCC is expressed as:

[0050] V P ∠δ P =Z g I L ∠(θ g +θ IL +δ L )+Z g I M ∠(θ g +θ IM +δ M )+V g

[0051] Among them, V g is the amplitude of the grid voltage, V P , δ P are the amplitude and phase of the PCC voltage, the grid impedance Z g =R g +jX g , the line impedance Z1=R1+jX1, and the line is approximately inductive, so

[0052] Furthermore, the voltage of the grid-following converter can be expressed as:

[0053] U L ∠θ L =I L Z1∠(θ1+θ IL +δ L )+V P ∠δ P

[0054] Among them, U L ,θ L are the amplitude and phase of the grid-following converter voltage respectively.

[0055] Furthermore, the q-axis voltage of the grid-following converter can be expressed as:

[0056] v qL =I L Z g sin(θ g +θ IL )+I L Z1sin(θ1+θ IL )

[0057] +Z g I M sin(θ g +θ IM +δ M -δ L )-V g sinδ L

[0058] V qL It can be broken down into two parts:

[0059] A refL =I L Z g sin(θ g +θ IL )+I L Z1 sin(θ1+θ IL )

[0060] A L =V g sinδ L +Z g I M sin(δ L -δ M -θ g -θ IM )

[0061] Among them, A refL It has nothing to do with the power angle of the grid-following converter and is a fixed value when the system line parameters are determined; A LIt is related to the power angle of the grid-type converter and is approximately a sinusoidal surface.

[0062] Active power P of grid-type converter M Expressed as:

[0063]

[0064] Among them, P M is approximated as a cosine surface.

[0065] Furthermore, in S1, the parallel system is set to have the grid-type converter as a current source in both normal and fault states, including setting the control reference current of the grid-type converter in both normal and fault states to be: Among them, i dLref is the d-axis control reference current of the grid-following converter, i qLref is the q-axis control reference current of the grid-following converter, I NL is the rated current of the grid-following converter, θ IL It is the angle of the grid-type converter's control current relative to the d-axis.

[0066] Specifically, such as Figure 3 As shown, the grid-type converter adopts phase-locked loop synchronization, and the specific algorithm formula is: L =∫(k pPLL v qL +k iPLL ∫v qL dt)dt; where δ L is the power angle of the grid-type converter, k pPLL and k iPLL The reference current of the current loop is given according to the grid requirements. Under normal circumstances, the grid-following converter usually only outputs active current. The current reference value i dqLref Set according to the power demand in steady state; in the event of a fault, the grid-following converter needs to provide reactive power to support the grid voltage, and i dqLref Control is performed to realize the distribution of active and reactive power. Using a unified form, i dqLref It can be written as:

[0067] Furthermore, the process of constructing the first transient analysis model corresponding to the grid-type converter in S2 includes: taking the power angle δ of the grid-type converter as an example, L The power angle δ of the grid-connected converter M With the horizontal and vertical axes as the axis, and the q-axis voltage of the grid-following converter as the axis, a first transient analysis model corresponding to the grid-following converter in the parallel system is constructed.

[0068] Furthermore, the process of determining the power angle stability region corresponding to the grid-type converter is as follows: the q-axis voltage expression v of the grid-type converter is converted to qL The part A that is not related to the power angle refL As the reference plane; the q-axis voltage expression v of the grid-type converter qL Part A related to the power angle L With reference plane A refL The intersection line is taken as the power angle stable area corresponding to the grid-type converter; among them, v qL Decomposed into two parts A refL and A L , I L is the output current amplitude of the grid-following converter, Z g is the grid impedance, θ g is the impedance angle of the grid-connected impedance, Z1 is the line impedance of the grid-connected converter connected to the common coupling point, θ1 is the impedance angle of the line impedance, V g is the grid voltage amplitude, I M is the output current amplitude of the grid-type converter, θ IM is the angle of the current of the grid-type converter relative to the d-axis.

[0069] Specifically, for an independent grid-following converter system, Figure 1 The grid-type converter branch in the grid-type converter can be ignored, so the q-axis voltage of the single-machine grid-type converter can be expressed as: v qL =I L Z g sin(θ g +θ IL )+I L Z1sin(θ1+θ IL )-V g sinδ L ; So v qL It can be broken down into two parts:

[0070] A refL =I L Z g sin(θ g +θ IL )+I L Z1sin(θ1+θ IL )

[0071] A L =V g sinδ L

[0072] It can be seen from the formula that for an independent grid-following converter, its A refLWith A L The expression is simple and is only related to its own power angle and current control angle.

[0073] The equivalent circuit of the grid-type converter is as follows: Figure 4 As shown in (a) in the figure. The solvability criterion of the phase-locked PLL is usually set to v qL = 0. Using a method similar to the transient analysis of synchronous generator SG, different V g Angle curve A of grid-following converter under value L (δ L )like Figure 4 As shown in (b). L It is a sine curve. Figure 4 (b) in the figure shows the power angle curve of the grid-following converter. refL With A L The left intersection of represents the stable equilibrium point SEP, while the right intersection represents the unstable equilibrium point UEP. After the fault occurs, if δ L The swing amplitude exceeds the grid-following converter angle limit δ corresponding to the unstable equilibrium point uL , which will lead to angle divergence and transient instability.

[0074] Furthermore, the normal state is set in S1 as The control reference current of the grid-type converter is: in, is the control current amplitude of the grid-type converter, I Mlim is the set current limit value, Indicates normal state, i dMref is the d-axis control reference current of the grid-type converter, i qMref is the q-axis control reference current of the grid-type converter, Indicates the q-axis current reference value output by the voltage loop, Indicates the q-axis current reference value output by the voltage loop. Further, the fault state is set in S1 as The control reference current of the grid-type converter is: (i dMref ,i qMref )=(i dMF ,i qMF );in, Indicates the fault state. The d-axis current setting value i of the grid-type converter in the fault state is dMF =I Mlim cos(θ IM ), the q-axis current setting value i of the grid-type converter under load fault condition qMF =I Mlim sin(θ IM ),θ IM is the angle of the grid-type converter current relative to the d-axis.

[0075] The grid-type converter adopts virtual synchronous VSG control synchronization. The specific algorithm formula of VSG control is:

[0076]

[0077] Among them, δ M is the power angle of the grid-type converter, P refM Indicates the active power reference value, P M Denotes the output active power of the grid-connected converter, J and D p are the inertia coefficient and the damping coefficient.

[0078] The current limit value of the grid-type converter is set to I Mlim , a typical current limiter is as follows:

[0079]

[0080] Among them, i dMF =I Mlim cos(θ IM ), i qMF =I Mlim sin(θ IM ),θ IM is the angle of the grid converter current relative to the d-axis. Represents the current reference value output by the voltage loop, and is the current amplitude.

[0081] Specifically, for an independent grid-type converter system, Figure 1 The grid-type converter branch in the circuit can be ignored, so the active power of the single-mechanism grid-type converter can be expressed as: It can be seen from the formula that its active power is only related to its own power angle and current control angle. The equivalent circuit of the grid-type converter is as follows: Figure 5 As shown in (a), before the fault, its external characteristics are equivalent to a voltage source, and after the fault, its external characteristics are equivalent to a current source. Figure 5 (b) shows the power angle curve of the grid-type converter. After the fault occurs, if δ M The swing amplitude exceeds the grid-type converter angle limit δ corresponding to the unstable equilibrium point uM , which will lead to angle divergence and transient instability.

[0082] Furthermore, the construction process of the second transient analysis model corresponding to the grid-type converter in S2 includes: taking the power angle δ of the grid-type converter as L The power angle δ of the grid-connected converter M The horizontal axis and vertical axis are the active power P of the grid-type converter. MThe z-axis is used to construct the second transient analysis model corresponding to the grid-type converter in the parallel system.

[0083] Furthermore, the process of determining the power angle stability region corresponding to the grid-type converter is as follows: the active power P of the grid-type converter is M The intersection line with the reference plane corresponding to the power setting value is taken as the power angle stable region corresponding to the grid-type converter.

[0084] Figure 6 The phasor diagram under the current limiting condition of the system is shown. L and P M The expression is found to be that both are about the power angle δ L and δ M When the system parameters are determined, the other parameters are fixed values, so in the parallel system, A L and P M It will also be affected by the angle of another converter, making a three-dimensional power angle surface such as Figure 7 As shown. L Approximately a sinusoidal surface, P M It is approximately a cosine surface. The upper limit of the power angle of the two converters δ uL and δ uM is no longer a fixed value, but changes due to coupling. L and A refL The intersection relationship, P M and P refM The intersection relationship of Figure 8 The power angle stable region of the parallel system is shown.

[0085] When the grid voltage V g When the drop value changes from 0.5pu to 0.9pu, observe the power angle trajectory of the system's critical stability removal process, as shown in the figure below: Figure 9 As shown. When V g When the drop is small, δ L The oscillation amplitude is small and far away from its angular limit δ uL With V g As the drop increases, δ L The oscillation amplitude also increases, and the corresponding critical clearing time gradually decreases. g When the drop is significant, δ L The swing approaches the angle limit δ uL , which indicates the risk of instability. Overall, as V g As the drop degree increases, the transient stability of the system gradually changes from being determined by the grid-forming converter to being determined by the grid-following converter.

[0086] For a single-machine system, the maximum deceleration area DA is usually used to evaluate the transient stability margin. Assume that the steady-state angle of the single-machine grid-following converter is δ sL , the steady-state angle of the single-mechanism grid converter is δ sM Then the maximum deceleration area DA L and DA M It can be expressed as:

[0087]

[0088] For the parallel grid-type converter-grid-type converter system, since the two-dimensional angle curve is expanded into a three-dimensional angle surface, the maximum deceleration area DA can no longer fully describe the angle deceleration area. Therefore, the maximum deceleration volume DV is used to characterize the relevant characteristics. L and DV M The calculation formula is:

[0089]

[0090] DV L and DV M It covers all the areas where the system’s angle trajectory may pass without losing stability, such as Figure 10 shown.

[0091] Further, using DV L and DV M Study the influence of system parameters on stability. Change the line parameters of grid-following converter, grid-forming converter and grid impedance parameters to obtain DV under different working conditions. L and DV M As shown in Table 1.

[0092] Table 1: DV under different system parameters L and DV M

[0093]

[0094] When the grid impedance Z g When it increases, it means that the grid strength becomes weaker, and the maximum deceleration volume DV corresponding to the grid converter L The maximum deceleration volume DV corresponding to the grid converter M This reduces the transient stability margins of both the grid-following and grid-forming converters, making the system more susceptible to transient instability.

[0095] When the transmission line impedance Z1 of the grid-following converter increases, that is, the transmission line of the grid-following converter becomes longer, it will cause the steady-state power angle δ of the grid-following converter to sL For the grid-following converter, Z1 increases so that its reference plane A refLIncrease, leading to DV L For the grid-type converter, δ sL However, due to the high power angle limit of the grid-following converter, this effect is not significant and only causes DV M Slightly reduced.

[0096] When the transmission line impedance Z2 of the grid-type converter increases, that is, the transmission line of the grid-type converter becomes longer, the steady-state power angle δ of the grid-type converter will be sM , and also reduce its deceleration area. This will cause DV L and DV M All decreased.

[0097] Therefore, using this transient margin quantification indicator, it is found that the grid impedance Z g Increasing will significantly reduce the transient stability of the two converters. Increasing the converter line impedance Z1 or Z2 will significantly reduce the transient stability of its own converter and slightly reduce the transient stability of the coupled converter.

[0098] Example 2

[0099] This embodiment provides a transient stability analysis device for a new energy power system. The new energy power system is a parallel system consisting of a grid-following converter and a grid-forming converter, which are connected to a common coupling point via respective lines and corresponding filters and then connected to the grid via grid impedance. The transient stability analysis device includes a setting module, a characterization module, a determination module, and an analysis module.

[0100] The setting module is used to set the parallel system's grid-type converters to be current sources in both normal and fault states; set the parallel system's grid-type converters to be voltage sources in normal states and switch to current sources in fault states.

[0101] The characterization module is used to construct a first transient analysis model corresponding to the grid-type converter represented by the surface and a second transient analysis model corresponding to the grid-type converter represented by the surface using the circuit equation of the parallel system.

[0102] The determination module is configured to use the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as the power angle stable regions of their respective converters.

[0103] The analysis module is used to analyze the actual power angle of the parallel system under different grid voltage drops. If the actual power angle exceeds the power angle stability region corresponding to the grid-following converter, the grid-following converter is considered unstable. If the actual power angle exceeds the power angle stability region corresponding to the grid-forming converter, the grid-forming converter is considered unstable, thereby determining the transient weak converter corresponding to different grid voltage drops.

[0104] Example 3

[0105] This embodiment provides a transient stability analysis system for a new energy power system, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the transient stability analysis method provided in Example 1 are implemented.

[0106] Example 4

[0107] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the transient stability analysis method provided in Embodiment 1 are implemented.

[0108] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A transient stability analysis method for a new energy power system, characterized in that: The new energy power system is a parallel system consisting of a grid-forming converter and a grid-following converter, which are connected to a common coupling point through their respective lines and corresponding filters and then connected to the grid through the grid impedance. The transient stability analysis method includes: S1: setting the grid-connected converter of the new energy power system to be a current source in both normal and fault states; setting the grid-connected converter of the new energy power system to be a voltage source in the normal state and to be a current source in the fault state; S2: constructing a first transient analysis model corresponding to the grid-forming converter represented by a curved surface and a second transient analysis model corresponding to the grid-following converter represented by a curved surface using the circuit equation of the new energy power system; S3: using the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as the power angle stable regions of their respective converters; S4: Analyze the actual power angle of the new energy power system when different grid voltage drops occur; if the actual power angle exceeds the power angle stability region corresponding to the grid-forming converter, it is regarded as the grid-forming converter being unstable; if the actual power angle exceeds the power angle stability region corresponding to the grid-following converter, it is regarded as the grid-following converter being unstable, thereby determining the transient weak converter corresponding to the different grid voltage drops.

2. The transient stability analysis method of the new energy power system according to claim 1, characterized in that: The step S1 sets the grid-type converter of the new energy power system to be a current source in both the normal state and the fault state, including setting the control reference current of the grid-type converter in both the normal state and the fault state to be: Among them, i dLref is the d-axis control reference current of the grid-following converter, i qLref is the q-axis control reference current of the grid-following converter, I NL is the rated current of the grid-following converter, θ IL is the angle of the control current of the grid-following converter relative to the d-axis.

3. The transient stability analysis method of the new energy power system according to claim 2, characterized in that: The process of constructing the first transient analysis model corresponding to the grid-type converter in S2 includes: The power angle δ of the grid-following converter L The power angle δ of the grid-connected converter M As the horizontal and vertical axes, the q-axis voltage of the grid-following converter is taken as the z-axis, and a first transient analysis model corresponding to the grid-following converter in the new energy power system is constructed.

4. The transient stability analysis method of the new energy power system according to claim 3, characterized in that: The process of determining the power angle stability region corresponding to the grid-type converter is as follows: The q-axis voltage expression v of the grid-type converter is qL The part A that is not related to the power angle refL As the reference plane; the q-axis voltage expression v of the grid-type converter qL Part A related to the power angle L With the reference plane A refL The intersection line is used as the power angle stable area corresponding to the grid-type converter; in, v qL Decomposed into two parts A refL and A L , I L is the output current amplitude of the grid-following converter, Z g is the grid impedance, θ g is the impedance angle of the grid-connected impedance, Z1 is the line impedance of the grid-connected converter connected to the common coupling point, θ1 is the impedance angle of the line impedance, V g is the grid voltage amplitude, I M is the output current amplitude of the grid-type converter, θ IM is the angle of the current of the grid-type converter relative to the d-axis.

5. The transient stability analysis method of the new energy power system according to claim 1, characterized in that: In S1, the normal state is set to The control reference current of the grid-type converter is: in, is the control current amplitude of the grid-type converter, I Mlim is the set current limit value, i dMref is the d-axis control reference current of the grid-type converter, i qMref is the q-axis control reference current of the grid-type converter, Indicates the q-axis current reference value output by the voltage loop, Indicates the q-axis current reference value output by the voltage loop.

6. The transient stability analysis method of the new energy power system according to claim 5, characterized in that: The fault state is set in S1 as The control reference current of the grid-type converter is: dMref ,i qMref )=(i dMF ,i qMF ); Wherein, the grid-type converter carries the d-axis current setting value i under the fault state dMF =I Mlim cos(θ IM ), the grid-type converter carries the q-axis current setting value i under the fault state qMF =I Mlim sin(θ IM ),θ IM is the angle of the current of the grid-type converter relative to the d-axis.

7. The transient stability analysis method of the new energy power system according to claim 6, characterized in that: The process of constructing the second transient analysis model corresponding to the grid-type converter in S2 includes: The power angle δ of the grid-following converter L The power angle δ of the grid-connected converter M The horizontal axis and vertical axis are the active power P of the grid-type converter. M The z-axis is used to construct a second transient analysis model corresponding to the grid-connected converter in the new energy power system.

8. The transient stability analysis method of the new energy power system according to claim 7, characterized in that: The process of determining the power angle stable region corresponding to the grid-type converter is as follows: the active power P of the grid-type converter is M The intersection line with the reference plane corresponding to the power setting value is used as the power angle stable region corresponding to the grid-type converter.

9. A transient stability analysis device for a new energy power system, characterized in that: The new energy power system is a parallel system consisting of grid-connected converters and grid-following converters that are connected to a common coupling point through their respective lines and corresponding filters, and then connected to the grid through grid impedance. The transient stability analysis device comprises: A setting module is used to set the grid-following converter of the new energy power system to be a current source in both a normal state and a fault state; set the grid-forming converter of the new energy power system to be a voltage source in the normal state and to be switched to a current source in the fault state; A characterization module, configured to construct a first transient analysis model corresponding to the grid-forming converter represented by a curved surface and a second transient analysis model corresponding to the grid-following converter represented by a curved surface using a circuit equation of the new energy power system; a determination module, configured to use the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as power angle stability regions of their respective converters; An analysis module is used to analyze the actual power angle of the new energy power system when different grid voltage drops occur; if the actual power angle exceeds the power angle stability region corresponding to the grid-forming converter, it is considered that the grid-forming converter is unstable; if the actual power angle exceeds the power angle stability region corresponding to the grid-following converter, it is considered that the grid-following converter is unstable, thereby determining the transient weak converter corresponding to the different grid voltage drops.

10. A transient stability analysis system for a new energy power system, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

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