A transient stability analysis method, device and system of a new energy power system

Abstract

This invention discloses a transient stability analysis method, apparatus, and system for new energy power systems, belonging to the field of new energy power generation technology. It sets the grid-connected converter as a voltage source under normal conditions and switches to a current source under fault conditions. It utilizes surface characterization to represent a first transient analysis model corresponding to the grid-connected converter and a second transient analysis model corresponding to the grid-connected converter, thereby determining the power angle stability region of each type of converter. It analyzes the actual power angle of the new energy power system under different grid voltage drops, observes the power angle swing trajectory of each converter, and thus accurately reflects the transiently weak converters corresponding to different grid voltage drops. Compared with existing technologies, this application can accurately characterize the power angle stability region of each grid-connected converter, simulate new energy power systems under various fault conditions, provide a strong basis for early prevention of system instability, and improve the reliability of new energy power system operation.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, and more specifically, relates to a transient stability analysis method, apparatus and system for a new energy power system. Background Technology

[0002] Against the backdrop of a global push for clean energy development, the penetration rate of new energy sources in power systems is increasing daily. In this process, grid-connected converters are widely used due to their crucial role in integrating new energy sources into the grid. However, the reliance of grid-connected converters on phase-locked loops (PLLs) makes them vulnerable to weak grid environments. In contrast, grid-connected converters can actively support the grid, enhancing grid stability by establishing stable frequency and voltage. However, when grid-connected and grid-connected converters operate in parallel, the coupling between them in dynamic processes becomes complex. This coupling may lead to power angle divergence, causing system instability.

[0003] Currently, there are many shortcomings in addressing the transient power angle stability problem of converters. Existing research mostly focuses on single converter systems, failing to fully consider the coupling characteristics of grid-connected and parallel-connected converters, and lacking accurate coupling modeling methods for parallel systems. Furthermore, in assessing system stability, there is a lack of effective means to quantify stability margins, making it difficult to accurately determine the stability level of the system.

[0004] Therefore, in order to ensure the reliable operation of new energy power systems, there is an urgent need for a systematic method that can comprehensively consider coupling effects, accurately define stability boundaries, and achieve optimized control, so as to solve the transient stability problem when grid-connected converters are running in parallel and promote the efficient application of new energy in the power field. Summary of the Invention

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

[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 grid-connected converters and grid-connected converters connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power grid via grid impedance. The transient stability analysis method includes:

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

[0008] S2: 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 using the circuit equations of the new energy power system.

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

[0010] S4: Analyze the actual power angle of the new energy power system when the grid voltage drops. If the actual power angle exceeds the power angle stability region corresponding to the grid-type converter, the grid-type converter is considered to be unstable. If the actual power angle exceeds the power angle stability region corresponding to the grid-connected converter, the grid-connected converter is considered to be unstable, thereby determining the transient weak converter corresponding to the different grid voltage drops.

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

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

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

[0014] Furthermore, the process for 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 unrelated to the angle of attack refLAs a reference plane; the q-axis voltage expression v of the grid converter will be used. qL Part A related to the angle of attack L With the reference plane A refL The intersection line serves as the power angle stability region corresponding to the grid-type converter; wherein... v qL Decomposed into two parts A refL and A L , I L To match the amplitude of the output current of the grid-connected converter, Z g For grid connection impedance, θ g Z1 is the impedance angle of the grid-connected impedance, Z1 is the line impedance connected to the common coupling point of the grid-connected converter, θ1 is the impedance angle of the line impedance, and V g I represents the voltage amplitude of the power grid. M θ represents the amplitude of the output current of the grid-connected converter. IM The angle of the current in the grid-type converter relative to the d-axis.

[0015] Furthermore, in S1, the normal state is set as... The control reference current for the grid-type converter is: in, I is the control current amplitude of the grid-type converter. Mlim The set rate limit value, Indicates the normal state, i dMref i is the d-axis control reference current for the grid-type converter. qMref The q-axis control reference current for the grid-type converter. This represents the q-axis current reference value output by the voltage loop. This represents the reference value of the q-axis current output by the voltage loop.

[0016] Furthermore, in S1, the fault state is set as follows: The control reference current of the grid-type converter is: (i dMref i qMref )=(i dMF i qMF );in, This indicates the fault state, and the grid-type converter carries the d-axis current setpoint i under the fault state. dMF =

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

[0018] Furthermore, the construction process of the second transient analysis model corresponding to the grid-type converter in S2 includes: using the power angle δ of the grid-type converter... L The power angle δ of the grid-type converter M Using the horizontal and vertical axes as the axes, and the active power P of the grid-type converter as the axis, M Using the z-axis as the z-axis, construct the second transient analysis model corresponding to the medium-voltage converter in the new energy power system.

[0019] Furthermore, the process for determining the power angle stability region corresponding to the grid-type converter is as follows: The active power P of the grid-type converter... M The intersection line with the reference plane corresponding to the power setting value is taken as the power angle stability 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 grid-connected converters and grid-connected converters connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power grid via grid impedance. The transient stability analysis device includes:

[0021] The setting module is used to set the grid-connected converter of the new energy power system to be a current source in both normal and fault states; and to set the grid-connected converter of the new energy power system to be a voltage source in the normal state and to switch to a current source in the fault state.

[0022] The characterization module is used 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 using the circuit equations of the new energy power system.

[0023] The determination module is used to take the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as the power angle stability regions of their respective converters;

[0024] The analysis module is used to analyze the actual power angle of the new energy power system when the 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-connected converter, it is considered that the grid-connected converter is unstable, thereby determining the transient weak converters 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, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the transient stability analysis method.

[0026] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0027] (1) This invention provides a transient stability analysis method for a new energy power system. It sets the grid-connected converters in both normal and fault states as current sources; sets the grid-connected converters in the normal state as voltage sources and switches them to current sources in the fault state; and utilizes surface characterization to represent the first transient analysis model corresponding to the grid-connected converter and the second transient analysis model corresponding to the grid-connected converter, thereby determining the power angle stability regions of each type of converter. It analyzes the actual power angle of the new energy power system under different grid voltage drops, observes the power angle swing trajectory of each converter, and thus accurately reflects the transiently weak converters corresponding to different grid voltage drops. Compared with existing stability analysis methods, this application can accurately characterize the power angle stability regions of each grid-connected converter, simulate new energy power systems under various fault conditions, provide a strong basis for early prevention of system instability, and improve the reliability of power system operation.

[0028] (2) In this scheme, the control reference current of the grid-connected converter under the normal state and the fault state is set as follows: The design incorporates current angle control of the d-axis and q-axis currents of the grid converter. Compared to existing technologies, this design enables control of the q-axis current during faults, resulting in reactive power output and voltage support during faults.

[0029] (3) This scheme uses the power angle δ of the grid-type converter. L The power angle δ of the grid-type converter M Using the horizontal and vertical axes as the axes and the q-axis voltage of the grid-connected converter as the z-axis, a first transient analysis model is constructed. This model considers the coupling effect of the grid-connected converter, which, compared to existing technologies, improves the accuracy of modeling and enhances the universality of the analysis conclusions.

[0030] (4) This scheme will follow the q-axis voltage expression v of the grid converter. qL Part A related to the angle of attack L With the reference plane A refL The intersection line is used as the power angle stability region corresponding to the grid-type converter; it takes into account the parts of the expression that are related to and unrelated to the power angle, and compared with the prior art, it can separate the expression and realize the simplification of the analysis process.

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

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

[0033] (7) This scheme uses the power angle δ of the grid converter. L The power angle δ of the grid-type converter M Using the horizontal and vertical axes as the axes, and the active power P of the grid-type converter as the axis, M A second transient analysis model is constructed with the z-axis as the reference axis. The influence of coupling with the grid converter is taken into account. Compared with the existing technology, it can improve the accuracy of modeling and improve the universality of the analysis conclusions.

[0034] (8) This scheme will use the active power P of the grid-type converter. M The intersection line with the reference plane corresponding to the power setpoint is taken as the power angle stability region corresponding to the grid-type converter. The influence of current limiting of the grid-type converter on the active power surface shape is considered. Compared with the prior art, it can accurately quantify the power angle boundary of the grid-type converter and provide guidance for the analysis of system transient stability. Attached Figure Description

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

[0036] Figure 2 This is a flowchart of the transient stability analysis method for a new energy power system in Embodiment 1 of the present invention;

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

[0038] Figure 4 This is the equivalent circuit and power angle curve diagram of the single-unit grid converter in Embodiment 1 of the present invention;

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

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

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

[0042] Figure 8 This is a schematic diagram of the power angle stability region of the new energy power system in Embodiment 1 of the present invention;

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

[0044] Figure 10 The maximum deceleration volume DV in Embodiment 1 of the present invention L and DV M A schematic diagram. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be 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 illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0046] Example 1

[0047] This 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 grid-connected converters and grid-connected converters connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power grid via grid impedance. Specifically, as follows... Figure 1 As shown, the grid-type converter uses an L-type converter. f1 and C f1 The LC filter is then connected to the common coupling point PCC via line impedance Z1; the grid-type converter uses an LC filter... f2 and C f2 The LC filter is then connected to the PCC via line impedance Z2.

[0048] Furthermore, such as Figure 2As shown, the transient stability analysis method includes the following steps: S1: Set the grid-connected converter as a current source in both normal and fault states of the parallel system; set the grid-connected converter as a voltage source in normal state and switch to a current source in fault state; S2: Construct a first transient analysis model corresponding to the grid-connected converter and a second transient analysis model corresponding to the grid-connected converter, represented by a surface, using the circuit equations of the parallel system; S3: Take the intersection lines of the first and second transient analysis models with their respective reference planes as the power angle stability regions of their respective converters; 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-connected converter, it is considered that the grid-connected converter is unstable; if the actual power angle exceeds the power angle stability region corresponding to the grid-connected converter, it is considered that the grid-connected converter is unstable, thereby determining the transiently weak converter corresponding to different grid voltage drops.

[0049] Specifically, for parallel systems corresponding to grid-connected converters and network-type converters, in the event of a fault, the network-type converter can be equivalent to a current amplitude and phase of I. M and (δ) M +θ IM The current source is equivalent to a grid-type converter with current amplitude and phase I. L and (δ) L +θ IL The current source of PCC can be further represented by the circuit equations, and the voltage of PCC can be 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 It is the amplitude of the grid voltage, V P δ P These represent the amplitude and phase of the PCC voltage, and the mains impedance Z. g =R g +jX g The line impedance Z1 = R1 + jX1, and the line is approximately inductive, therefore

[0052] Furthermore, the voltage of the grid-connected 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 These are the amplitude and phase of the voltage of the grid-connected converter, respectively.

[0055] Furthermore, the q-axis voltage of the grid 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 The power angle is independent of the grid-connected converter and is a constant value when the system line parameters are determined; A LIt is related to the power angle of the grid converter and is approximately a sinusoidal surface.

[0062] The active power P of the grid-type converter M Represented as:

[0063]

[0064] Among them, P M It is approximately a cosine surface.

[0065] Furthermore, S1 sets the parallel system to be a current source for both the grid-connected converter and the network converter under normal and fault conditions, including: setting the control reference current of the grid-connected converter under normal and fault conditions as follows: Among them, i dLref To control the d-axis reference current of the grid-type converter, i qLref To match the q-axis control reference current of the grid-type converter, I NL To match the rated current of the grid-connected converter, θ IL It refers to the angle of the control current of the grid converter relative to the d-axis.

[0066] Specifically, such as Figure 3 As shown, the grid converter uses a phase-locked loop for synchronization. The specific algorithm formula is: δ L =∫(k pPLL v qL +k iPLL ∫v qL dt)dt; where δ L It is related to the power angle of the grid converter, k pPLL and k iPLL These are the proportional control parameters and integral control parameters of the phase-locked loop (PLL). The reference current for the current loop is given according to grid requirements. Under normal circumstances, grid-connected converters typically only output active current, and the current reference value i... dqLref The power requirements are set according to steady-state power demand; under fault conditions, the grid-connected converter needs to provide reactive power to support the grid voltage, requiring adjustments to i. dqLref Control is implemented to distribute active and reactive power. A unified approach is adopted, i dqLref It can be written as:

[0067] Furthermore, the construction process of the first transient analysis model corresponding to the grid converter in S2 includes: using the power angle δ of the grid converter... L The power angle δ of the grid-type converter M Using the horizontal and vertical axes as the axes and the q-axis voltage of the grid converter as the z-axis, we construct the first transient analysis model corresponding to the grid converter in the parallel system.

[0068] Furthermore, the process for 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 unrelated to the angle of attack refL As a reference plane; the q-axis voltage expression v of the grid converter will be used. qL Part A related to the angle of attack L With reference plane A refL The intersection line serves as the power angle stability region corresponding to the grid converter; among which... v qL Decomposed into two parts A refL and A L , I L To match the amplitude of the output current of the grid-connected converter, Z g For grid connection impedance, θ g Z1 is the impedance angle of the grid-connected impedance, Z1 is the line impedance connected to the common coupling point of the grid-connected converter, θ1 is the impedance angle of the line impedance, and V g I represents the voltage amplitude of the power grid. M θ represents the amplitude of the output current of the grid-connected converter. IM The angle of the current in the grid-type converter relative to the d-axis.

[0069] Specifically, for an independent grid-following converter system, Figure 1 The branches of the grid-type converter in the circuit can be neglected. Therefore, the q-axis voltage of the single-unit 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 Therefore, 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] As can be seen from the formula, for an independent grid-connected converter, its A refLWith A L The expression is simple and only depends on its own power angle and current control angle.

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

[0074] Furthermore, the normal state is set in S1 as The control reference current for the grid-type converter is: in, I represents the control current amplitude of the grid-connected converter. Mlim The set rate limit value, Indicates the normal state, i dMref For the d-axis control reference current of the grid-type converter, i qMref The q-axis control reference current for the grid-type converter. This represents the q-axis current reference value output by the voltage loop. This represents the reference value of the q-axis current output by the voltage loop. Furthermore, the fault state is set in S1 as follows: The control reference current for the grid-type converter is: (i dMref i qMref )=(i dMF i qMF );in, Indicates the fault state; the d-axis current setpoint i of the grid-type converter under fault conditions. dMF =I Mlim cos(θ IM The setpoint i of the q-axis current under fault conditions in a grid-type converter. qMF =I Mlim sin(θ IM ), θ IM It is the angle of the current in a grid-type converter relative to the d-axis.

[0075] Grid-type converters use virtual synchronous VSG control for synchronization. The specific algorithm formula for VSG control is as follows:

[0076]

[0077] Where, δ M For the power angle of the grid-type converter, P refM P represents the active power reference value. M J and D represent the output active power of the grid-type converter. p These are the inertia coefficient and the damping coefficient.

[0078] Set the current limiting value of the grid converter 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 It is the angle of the current in a grid-type converter relative to the d-axis. This represents the current reference value output by the voltage loop, while It is the current amplitude.

[0081] Specifically, for a standalone grid-type converter system, Figure 1 The branches of the grid-type converter in the circuit can be neglected. Therefore, the active power of a single-mechanism grid-type converter can be expressed as: As can be seen from the formula, 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 a fault occurs, if δ M The oscillation amplitude exceeded the angle limit δ of the grid converter corresponding to the unstable equilibrium point. uM This will lead to angular divergence and transient instability.

[0082] Furthermore, the construction process of the second transient analysis model corresponding to the grid-type converter in S2 includes: using the power angle δ of the grid-type converter... L The power angle δ of the grid-type converter M The horizontal and vertical axes represent the active power P of the grid-type converter. MUsing the z-axis as the z-axis, construct the second transient analysis model corresponding to the medium-scale converter in the parallel system.

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

[0084] Figure 6 The phasor diagram of the system under current-limited conditions is shown. Observe A. L and P M The expressions reveal that both are related to the work angle δ. L and δ M The expression for A is such that when the system parameters are determined, the other parameters are constants. Therefore, in a parallel system, A... L and P M It will also be affected by the angle of another converter, resulting in a three-dimensional power angle surface such as... Figure 7 As shown. A L Approximately a sinusoidal surface, P M It approximates a cosine surface. The upper limit of the power angle δ of the two converters. uL and δ uM It is no longer a fixed value, but changes due to coupling. Furthermore, according to A... L and A refL Intersection relation, P M and P refM The intersection relationship can be obtained as follows: Figure 8 The power angle stability region of the parallel system shown.

[0085] When the grid voltage V g When the drop value changes from 0.5 pu to 0.9 pu, observe the power angle trajectory of the system during the critical stability cut-off process, such as... Figure 9 As shown. When V g When the drop is small, δ L The oscillation amplitude is small and far from its angular limit δ. uL With V g The degree of drop increases, δ L The oscillation amplitude also increases accordingly, and the corresponding critical clearance time gradually decreases. When V g When the drop is significant, δ L The oscillation approaches the angular limit δ uL This indicates a risk of instability. Overall, with V g As the drop increases, the transient stability of the system gradually changes from being determined by the grid-type converter to being determined by the grid-following converter.

[0086] For stand-alone systems, the maximum reduction area DA is typically used to evaluate transient stability margin. Let the steady-state angle between the stand-alone and grid-type converters be δ. sL The steady-state angle of a single-mechanism grid converter is δ. sM So the maximum deceleration area DA L and DA M It can be represented as:

[0087]

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

[0089]

[0090] DV L and DV M It covers all regions that the system's angular trajectory might traverse without instability, such as Figure 10 As shown.

[0091] Furthermore, using DV L and DV M The influence of system parameters on stability was studied. By changing the line parameters of the grid-connected converter, the line parameters of the network-type converter, and the grid impedance parameters, the DV under different operating conditions was obtained. 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 An increase in voltage means a weakening of the power grid, which corresponds to the maximum deceleration volume DV of the grid converter. L The maximum reduction volume DV corresponding to the grid converter M Both are significantly reduced. This reduces the transient stability margin of both grid-connected and grid-connected converters, making the system more prone to transient instability.

[0095] When the transmission line impedance Z1 of the grid converter increases, i.e., when the transmission line of the grid converter becomes longer, it will cause the steady-state power angle δ of the grid converter to increase. sL Increase. For grid-connected converters, increasing Z1 makes its reference plane A... refLThe rise, which in turn led to DV L Significantly reduced. For grid-type converters, δ sL The increase in power angle reduces its deceleration range. However, due to the high power angle limit of the grid converter, this effect is not significant, only affecting DV. M Slightly reduced.

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

[0097] Therefore, using this transient margin quantification index, it was found that the grid impedance Z g Increasing the line impedance Z1 or Z2 will significantly reduce the transient stability of the two converters. Increasing the line impedance Z1 or Z2 of the converter will significantly reduce the transient stability of the converter itself, 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 grid-connected converters and grid-connected converters connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power 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 grid-type converter of the parallel system to be a current source in both normal and fault states; and to set the grid-type converter of the parallel system to be a voltage source in normal state and to switch to a current source in fault state.

[0101] The characterization module is used 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 using the circuit equations of the parallel system.

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

[0103] The analysis module is used to analyze the actual power angle of the parallel system when the 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.

[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 the processor executes the computer program to implement the steps of the transient stability analysis method provided in Embodiment 1.

[0106] Example 4

[0107] This embodiment provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the transient stability analysis method provided in Embodiment 1.

[0108] Those skilled in the art will readily understand 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 within 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 grid-connected converters and grid-connected converters connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power grid via grid impedance; the transient stability analysis method includes: S1: The grid-connected converter of the new energy power system is set to be a current source in both normal and fault states; the grid-connected converter of the new energy power system is set to be a voltage source in the normal state and to switch to a current source in the fault state. S2: 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 using the circuit equations of the new energy power system. S3: The intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes are taken as the power angle stability regions of their respective converters; S4: Analyze the actual power angle of the new energy power system when the grid voltage drops. If the actual power angle exceeds the power angle stability region corresponding to the grid-type converter, the grid-type converter is considered to be unstable. If the actual power angle exceeds the power angle stability region corresponding to the grid-connected converter, the grid-connected converter is considered to be unstable, thereby determining the transient weak converters corresponding to the different grid voltage drops. The construction process of the first transient analysis model corresponding to the grid converter in S2 includes: using the power angle of the grid converter... The power angle of the grid-type converter Using the horizontal and vertical axes as the axes and the q-axis voltage of the grid-connected converter as the z-axis, a first transient analysis model corresponding to the grid-connected converter in the new energy power system is constructed. The process for determining the power angle stability region corresponding to the grid-connected converter is as follows: The q-axis voltage expression of the grid-connected converter is... The part unrelated to the angle of attack As a reference plane; the q-axis voltage expression of the grid converter will be used. The part related to the angle of attack With the reference plane The intersection line serves as the power angle stability region corresponding to the grid-type converter; in, , Decomposed into two parts and , ; To match the amplitude of the output current of the grid-connected converter, For grid connection impedance, The impedance angle of this grid-connected impedance. To determine the line impedance at the common coupling point of the grid converter, The impedance angle of the line is the impedance angle. The voltage amplitude of the power grid. The amplitude of the output current of the grid-connected converter. The angle of the current in the grid-type converter relative to the d-axis.

2. The transient stability analysis method for new energy power systems as described in claim 1, characterized in that, In step S1, setting the grid-connected converter of the new energy power system to be a current source in both the normal state and the fault state includes: setting the control reference current of the grid-connected converter in both the normal state and the fault state as follows: ; in, The d-axis control reference current for the grid-connected converter. The q-axis control reference current for the grid-connected converter. I NL The rated current of the grid-connected converter is... It is the angle of the control current of the grid-type converter relative to the d-axis.

3. The transient stability analysis method for new energy power systems as described in claim 1, characterized in that, In S1, the normal state is set as The control reference current of the grid-type converter is: ; in, The value is the control current amplitude of the grid-type converter. I Mlim The set rate limit value, This serves as the d-axis control reference current for the grid-type converter. This serves as the q-axis control reference current for the grid-type converter. This represents the q-axis current reference value output by the voltage loop. This represents the reference value of the q-axis current output by the voltage loop.

4. The transient stability analysis method for a new energy power system as described in claim 3, characterized in that, The fault state is set as follows in S1 The control reference current of the grid-type converter is: ; The grid-type converter carries the d-axis current setpoint under the fault condition. i dMF = I Mlim cos( θ IM The grid-type converter carries the q-axis current setpoint under the fault condition. i qMF = I Mlim sin( θ IM ), θ IM It is the angle of the current in the grid-type converter relative to the d-axis.

5. The transient stability analysis method for a new energy power system as described in claim 4, characterized in that, The construction process of the second transient analysis model corresponding to the grid-type converter in S2 includes: With the power angle of the grid converter The power angle of the grid-type converter The horizontal and vertical axes are represented by the active power of the grid-type converter. P M Using the z-axis as the z-axis, construct the second transient analysis model corresponding to the medium-voltage converter in the new energy power system.

6. The transient stability analysis method for a new energy power system as described in claim 5, characterized in that, The process for determining the power angle stability region corresponding to the grid-type converter is as follows: The active power of the grid-type converter is... P M The intersection line with the reference plane corresponding to the power setting value is taken as the power angle stability region corresponding to the grid-type converter.

7. A transient stability analysis device for a new energy power system, characterized in that, For executing the transient stability analysis method according to any one of claims 1-6, the new energy power system is: a parallel system consisting of grid-type converters and grid-connected converters that are connected to a common coupling point via their respective lines and corresponding filters, and then connected to the power grid via the grid impedance. The transient stability analysis device includes: The setting module is used to set the grid-connected converter of the new energy power system to be a current source in both normal and fault states; and to set the grid-connected converter of the new energy power system to be a voltage source in the normal state and to switch to a current source in the fault state. The characterization module is used 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 using the circuit equations of the new energy power system. The determination module is used to take the intersection lines of the first transient analysis model and the second transient analysis model with their respective reference planes as the power angle stability regions of their respective converters; The analysis module is used to analyze the actual power angle of the new energy power system when the 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-connected converter, it is considered that the grid-connected converter is unstable, thereby determining the transient weak converters corresponding to the different grid voltage drops.

8. 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, it implements the steps of the method according to any one of claims 1 to 6.

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