Series-parallel system transient stability analysis and fault ride-through control method considering current limiting

Abstract

The invention discloses a series-parallel system transient stability analysis and fault ride-through control method considering current limiting, and belongs to the field of power fault analysis. In order to reveal an action mechanism of a current amplitude limiting and converter coupling effect on the transient synchronization stability of the hybrid system, the method comprises the following steps: firstly, considering the influence of control mode switching of a constructed network type converter, and establishing a transient analysis model of the hybrid system considering a current amplitude limiting link; then, based on a phase plane method, analyzing an action rule of converter control parameters on system transient stability, determining an optimal active power reference value and a saturation current phase angle of the grid-forming converter during a fault period, and proposing a fault ride-through control strategy according to the optimal active power reference value and the saturation current phase angle; and finally, verifying the correctness of theoretical analysis and the effectiveness of the proposed control strategy through multi-working-condition simulation.

Description

Technical Field

[0001] This invention relates to the field of power fault analysis, specifically to a method for transient stability analysis and fault ride-through control of a hybrid system taking current limiting into account. Background Technology

[0002] With the large-scale grid connection of new energy sources such as wind power and photovoltaics, the proportion of traditional synchronous generators in the power grid has been declining. Currently, the grid connection of new energy power plants mainly adopts grid-following voltage source converters (GFL-VSCs), relying on phase-locked loops (PLLs) to achieve synchronization with the grid voltage phase. This carries the risk of synchronization loss (LOS) under weak grid conditions. Introducing grid-forming voltage source converters (GFM-VSCs) to provide reliable voltage and frequency support for the system, and establishing a hybrid new energy system with both GFL-VSCs and GFM-VSCs, is the mainstream trend for improving the stability of high-proportion new energy power systems. However, GFM-VSCs are prone to transient synchronization instability under large disturbances, and their transient stability analysis is more complex than that of single GFM-VSC or GFL-VSC systems due to the complex coupling effects and transient control mode switching between converters in the hybrid system. Revealing the dynamic coupling mechanism between GFM-VSC and GFL-VSC under both non-triggered and triggered current-limiting conditions, and the impact of this coupling on the transient stability of the hybrid system, is of great significance for improving system stability. Summary of the Invention

[0003] To address the aforementioned shortcomings in the prior art, this invention provides a method for transient stability analysis and fault ride-through control of a hybrid system that takes current limiting into account.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting includes the following steps: S1. Establish a transient analysis model for a hybrid system of grid-connected converters and grid-connected converters, taking into account the current limiting circuit of the grid-connected converter. S2. Analyze the impact of converter control parameters on system transient stability based on the phase plane method; S3. Determine the optimal active power reference value and saturation current phase angle of the grid-type converter during the fault period based on the analysis results; S4. Design and implement an adaptive fault ride-through control strategy based on the optimal parameters.

[0005] Furthermore, the specific method for establishing the transient analysis model in S1 is as follows: System mathematical models for the grid-type converter under two operating conditions—untriggered current limiting and triggered current limiting—are established respectively. These models include a quasi-synchronous machine model for the grid-connected converter and a synchronous machine model for the grid-type converter. The active-frequency control equation and reactive-voltage control equation for the grid-type converter are respectively expressed as:

[0006]

[0007] In the formula, The virtual inertia of the grid-type converter. For the power angle of the grid-type converter, This is the active power reference value for grid-type converters. This refers to the actual output active power of the grid-type converter. The angular frequency of the power grid. The damping coefficient of the grid-type converter. This is the reactive power reference value for grid-type converters. This represents the actual reactive power of the grid-type converter. This is the voltage reference amplitude for the grid-type converter. The initial voltage value for the grid-type converter. This is the reactive power loop droop factor for a grid-type converter.

[0008] Furthermore, the specific method for analyzing the influence of converter control parameters based on the phase plane method in S2 is as follows: analyze the influence of the active power reference value and reactive power reference value of the grid-type converter, the output active current and reactive current of the grid-type converter on the transient stability of the system, and quantify the effect of parameter changes on the power angle balance point through the phase plane diagram; wherein, the equivalent mechanical power and equivalent output power of the grid-type converter are used to evaluate transient stability, and the calculation of the equivalent mechanical power involves the coupling terms of the grid-type converter.

[0009] Furthermore, the specific method for determining the optimal active power reference value and saturation current phase angle in S3 is as follows: the parameter value that minimizes the power angle deviation before and after the fault is found using the phase plane method; the optimal active power reference value is dynamically calculated based on the voltage ratio before and after the fault and the power coupling term, and the calculation formula is:

[0010] In the formula, This is a reference value for active power after the fault. and The voltage at the GFM-VSC terminal after the fault and the voltage of the mains grid after the fault; and The voltage at the GFM-VSC terminal before the fault and the voltage of the mains grid before the fault are given. This is the initial power reference value for the grid-type converter. This is a power coupling term.

[0011] Furthermore, the adaptive fault ride-through control strategy in S4 includes two modes: when the grid-type converter does not trigger current limiting, adaptive active power reference value control is used; when the grid-type converter triggers current limiting, adaptive saturation current phase angle control is used; wherein, the current limiting expression for the grid-type converter is:

[0012] In the formula, This is the current reference value for the grid-type converter after current limiting. The phase angle of the saturation current. This is the maximum allowable current for a grid-type converter. This is the initial current reference value for the grid-type converter.

[0013] Furthermore, the specific method of the adaptive saturation current phase angle control is as follows: using... q The q-axis priority current limiting with power angle compensation stage adjusts the saturated current phase angle based on the deviation between the power angle acquired at the moment of the fault and the current power angle, thereby reducing power angle oscillation; the q-axis priority current limiting corresponds to the saturated current phase angle. .

[0014] The present invention has the following beneficial effects: 1. When the grid voltage drops, regardless of whether the GFM-VSC triggers the limiting, the GFL-VSC has an optimal current ratio that can maintain its power angle constant before and after the fault. The GFM-VSC has an optimal active power reference value and an optimal saturation current phase angle that can maintain the power angle constant before and after the fault, effectively improving the transient stability of the hybrid system.

[0015] 2. The GFM-VSC adaptive fault ride-through control strategy proposed in this invention can achieve stable support under different levels of grid voltage drop. It can minimize power angle oscillation under both GFM-VSC non-triggered and current limiting conditions, effectively improving the transient stability of the hybrid system. Attached Figure Description

[0016] Figure 1 This is a topology diagram of the hybrid system of the present invention.

[0017] Figure 2 This is a control block diagram of GFL-VSC according to an embodiment of the present invention.

[0018] Figure 3 This is a control block diagram of GFM-VSC according to an embodiment of the present invention.

[0019] Figure 4 This is a diagram showing the relationship between current and power during LVRT in an embodiment of the present invention.

[0020] Figure 5 This is a diagram showing the current-power relationship after adjusting the reactive power droop coefficient in the GFM-VSC embodiment of the present invention.

[0021] Figure 6 This is an equivalent circuit diagram of a hybrid system according to an embodiment of the present invention.

[0022] Figure 7 This is a transient analysis model of the hybrid system under current limiting conditions when triggered and not triggered, according to an embodiment of the present invention.

[0023] Figure 8 This is a virtual power angle curve under different mechanical power in an embodiment of the present invention.

[0024] Figure 9 This is a phase plane diagram of each unit under different GFM-VSC power commands when current limiting is not triggered in an embodiment of the present invention.

[0025] Figure 10 This is a phase plane diagram of each unit under different GFL-VSC current injections when current limiting is not triggered in an embodiment of the present invention.

[0026] Figure 11 The virtual power angle curves of GFM-VSC under different saturation current phase angles in embodiments of the present invention are shown.

[0027] Figure 12 The diagram shows the phase plane of each unit under different GFM-VSC saturation current phase angles when current limiting is triggered according to an embodiment of the present invention.

[0028] Figure 13 This is a phase plane diagram of each unit under different GFL-VSC current injections when current limiting is triggered according to an embodiment of the present invention.

[0029] Figure 14 This is a block diagram of the GFM-VSC adaptive fault ride-through control in an embodiment of the present invention.

[0030] Figure 15 This is a virtual power angle curve for the GFM-VSC embodiment of the present invention.

[0031] Figure 16 The figures are simulation graphs under different GFM-VSC power commands when current limiting is not triggered in the embodiments of the present invention.

[0032] Figure 17 The figures are simulation results of different GFL-VSC current injections when current limiting is not triggered in the embodiments of the present invention.

[0033] Figure 18 Different methods are used to trigger rate limiting in different embodiments of the present invention. The following is a simulation graphic.

[0034] Figure 19 The simulation results are shown below for different GFL-VSC current injections when current limiting is triggered according to an embodiment of the present invention.

[0035] Figure 20 These are simulation graphs of a hybrid system under different control strategies when current limiting is not triggered, according to embodiments of the present invention.

[0036] Figure 21 The figures show simulation diagrams of a hybrid system under different control strategies when current limiting is triggered according to an embodiment of the present invention.

[0037] Figure 22 This is a schematic diagram showing the stability of the equilibrium point of the hybrid system under different initial conditions according to an embodiment of the present invention.

[0038] Figure 23 The different current limiting triggering conditions under extremely weak and strong power grids in the embodiments of the present invention are as follows: The following is a simulation graphic.

[0039] Figure 24 The figures show simulation graphs of different GFM-VSC power commands under extremely weak and strong power grids without current limiting triggered, according to embodiments of the present invention.

[0040] Figure 25 The simulation graphs show the current injection of different GFL-VSCs under extremely weak and strong power grids without current limiting triggered, according to embodiments of the present invention.

[0041] Figure 26 The simulation graphs show the current injection of different GFL-VSCs when current limiting is triggered under extremely weak and strong power grids in embodiments of the present invention. Detailed Implementation

[0042] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0043] A method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting includes the following steps: S1. Establish a transient analysis model for a hybrid system of grid-connected converters and grid-connected converters, taking into account the current limiting circuit of the grid-connected converter. Figure 1 This is the topology diagram of the hybrid system studied in this paper. Among them, and These are the inductor current phasors for GFL-VSC and GFM-VSC, respectively. and These are the port voltage phasors for GFL-VSC and GFM-VSC, respectively. This refers to the output current phasor of the GFM-VSC. This refers to the voltage phasor at the point of common coupling (PCC). For grid voltage phasors, and These are the line impedances from the grid-connected / network-connected converter to the PCC, respectively. The equivalent impedance of the power grid. and These are the filter inductors for the grid-connected / grid-connected converters. and These are the equivalent resistances of the grid-connected / network-connected converter filters, respectively. and These are the filter capacitors for the grid / network converter, respectively.

[0044] Figure 2 This is the control block diagram for GFL-VSC. Among them, and For GFL-VSC port voltage phasors d Axial components and q Axial components, and GFL-VSC inductor current phasor d Axial components and q Axial components, and These are the proportional and integral coefficients of the phase-locked loop (PLL), respectively. s For differential operators, and These are the grid voltage angular frequency and the GFL-VSC voltage angular frequency, respectively. For GFL-VSC voltage phase angle, and These are the current reference phasors of GFL-VSC. d Axial components and q Axial components, and These are the current reference phasors after GFL-VSC triggers LVRT. d Axial components and q Axial components, and These represent the actual active power and reactive power output of the GFL-VSC, respectively. and These are the active power reference value and reactive power reference value of GFL-VSC, respectively. PWM is the pulse width modulator, and PI is the proportional-integral regulator.

[0045] Depend on Figure 2 It can be seen that the GFL-VSC achieves synchronization with the power grid based on a phase-locked loop and employs a dual-closed-loop vector control based on generator terminal voltage orientation. Under non-fault conditions, the corresponding power is obtained through the outer power loop. dq Axis current reference phasor , j The unit is imaginary; when a grid fault occurs, the GFL-VSC will enter Low Voltage Ride Through (LVRT) mode, at which point the current reference value will switch to the reference phasor triggered by LVRT. The reference current command is calculated directly based on the low-voltage ride-through requirements. Figure 2 middle, k p,L and k i,L These are the proportional gain and integral gain of the PLL, respectively. θ L The phase angle is the phase angle of the phase-locked loop, and the other variables are shown in Table 1.

[0046] Table 1. List of symbols for GFL-VSC / GFM-VSC hybrid systems

[0047] Since the bandwidth of the current loop is much larger than that of the PLL, the dynamic characteristics of the current loop can be ignored in the analysis of the transient synchronization stability of GFL-VSC. Therefore, in terms of external characteristics, the GFL-VSC can be regarded as a controlled current source. This paper uses the grid voltage as a reference and the GFL-VSC power angle... δ L = θ L Its PLL dynamic equation can be expressed as: (1) Figure 3 This is the control block diagram for GFM-VSC. Among them, and These represent the actual active power and reactive power output of the GFM-VSC, respectively. and These are the active power reference value and reactive power reference value for GFM-VSC, respectively. The damping coefficient is GFM-VSC. J For GFM-VSC virtual inertia, For GFM-VSC voltage phase angle, This refers to the reactive power voltage regulation coefficient of GFM-VSC. This refers to the rated voltage amplitude of the GFM-VSC. This is the reference amplitude for the GFM-VSC voltage. and These are the voltage reference phasors of GFM-VSC, respectively. d Axial components and q Axial components, and These are the current reference phasors of the GFM-VSC. d Axial components and q Axial components, and These are the current reference phasors after current limiting by GFM-VSC. d Axial components and q Axial components, and These are the voltage reference phasors after current limiting by GFM-VSC. d Axial components and q Axial components, The current saturation phase angle for GFM-VSC is... This is the maximum allowable current for the GFM-VSC.

[0048] Depend on Figure 3 It can be seen that GFM-VSC adopts typical virtual synchronous machine control, including an external power control loop and internal voltage and current control loops. The power control loop includes active and reactive power control loops, with the active power control loop simulating the rotor motion process of a synchronous generator to generate phase angles. The reactive power control loop generates a voltage reference amplitude based on the output reactive power. .

[0049] Since the response speed of the inner voltage and current loop of the GFM-VSC is much faster than that of the external power loop, the dynamic characteristics of the internal voltage and current control loop can be ignored when analyzing the transient synchronization stability problem caused by the power loop. Therefore, in terms of external characteristics, GFM-VSC can be regarded as having an amplitude of The phase angle is The voltage source. This article uses the grid voltage as a reference and the power angle of the GFM-VSC. The active-frequency and reactive-voltage control equations are shown in equations (2) and (3), respectively: (2) (3) Currently, current limiting methods mainly include virtual impedance current limiting and current saturation strategy current limiting. Current saturation strategy current limiting can be further divided into ring current limiting and priority current limiting. This paper adopts a priority-based current limiting method, whose saturation current... The expression is shown in equation (4): (4) In the formula: This refers to the maximum allowable current of the GFM-VSC. Saturation current and d The included angle of the shaft is adjusted. Saturation current can be achieved in current-limiting mode. d - q Component allocation, At that time d Axis-priority current limiting method, when At that time q Axis-priority current limiting method, appropriate selection It can effectively improve the transient stability of GFM-VSC.

[0050] Different countries use different LVRT standards for converters, but generally speaking, during LVRT, the converter needs to generate additional reactive current, and reactive current has a higher priority than active current. This article defines the output reactive current as negative, and the converter reactive current... I q The requirements are as follows: (5) In the formula: The dynamic reactive current proportionality coefficient is recommended to be between 1.5 and 3; this paper uses a value of 3. The maximum allowable current of the converter is 1.05 pu; This represents the initial reactive current of the converter. The voltage at the converter's grid connection point corresponds to... Figure 1 In and .

[0051] To meet reactive current requirements, when the converter output current approaches the converter's maximum allowable current during LVRT. At this time, its active current needs to be derated accordingly to ensure the normal output of reactive current. Further power calculations can then be performed to determine... Figure 4 The diagram shows the relationship between the current and power output by the converter during LVRT.

[0052] Figure 4 middle, The critical voltage at which the output reactive current reaches the maximum allowable current of the converter is determined by [the following formula is missing from the original text]. , and This is a joint decision. For GFL-VSC, the active and reactive currents can be directly controlled to meet LVRT requirements. This is achieved by adjusting the reactive power loop droop factor. To meet the reactive current requirements during LVRT, the original reactive loop structure is retained. The power-current relationship during GFM-VSC faults is as follows: Figure 5 As shown, Figure 5 The national standard reactive current range indicated by the winning bid is the reactive current proportional coefficient. Current range at that time The initial output of GFM-VSC is reactive.

[0053] For GFM-VSC, without triggering current limiting, the external power loop structure and active and reactive power reference values ​​need to be adjusted to meet LVRT requirements. The actual active and reactive power reference values ​​for GFM-VSC are as follows: (6) (7) In the formula, , This is the initial power reference value for GFM-VSC.

[0054] During a fault, the external characteristics of the GFL-VSC are equivalent to a current source, while the external characteristics of the GFM-VSC are equivalent to a voltage source when current limiting is not triggered, and equivalent to a current source after current limiting is triggered. The equivalent circuit of the hybrid system is as follows: Figure 6 As shown, we will now analyze two cases.

[0055] When rate limiting is not triggered, for GFL-VSC, by Figure 6 In part (a), the terminal voltage phasor of GFL-VSC can be derived based on the superposition theorem and the principle of coordinate transformation. q Axis component expression: (8) In the formula: The terminal voltage phasor of GFL-VSC when GFM-VSC does not trigger current limiting q Axis component expressions; For GFL-VSC inductor current; The impedance value of the GFL-VSC line. For GFL-VSC line impedance angle; For GFL-VSC impedance angle; , and For computational load, , , , , and They are respectively , and The phase angle; The phase angle of the grid voltage; The phase angle of the GFM-VSC voltage; The phase angle of the GFL-VSC voltage; , and This refers to the analysis parameters when GFM-VSC does not trigger current limiting, where The voltage drop term is generated by the interaction between the GFL-VSC's self-injected current and the line impedance, and is defined as the self-impedance voltage drop term. This term is generated by the coupling between GFL-VSC and GFM-VSC through the transmission network and is defined as the coupling impedance voltage drop term. The term reflecting the impact of the power grid on the terminal voltage of the GFL-VSC is defined as the power grid voltage coupling term.

[0056] Substituting equation (8) into equation (1), we can derive a synchronous-like model characterizing the dynamics of GFL-VSC: (9) In the formula: and The equivalent inertia coefficient and equivalent damping coefficient of the GFL-VSC when the GFM-VSC does not trigger current limiting; , and These are the GFL-VSC power angle, the first derivative of the GFL-VSC power angle, and the second derivative of the GFL-VSC power angle, respectively. The power angle deviation between GFM-VSC and GFL-VSC is represented by its value. = , for The first derivative; and These represent the equivalent mechanical power and equivalent output power of the GFL-VSC when the GFM-VSC is not triggering current limiting, but essentially they are still the line impedance voltage drop and the grid voltage. q Axial components; D ML1 The equivalent cross-damping coefficient of GFL-VSC when GFM-VSC does not trigger current limiting; The phasor of the GFL-VSC inductor current when the GFM-VSC is not triggered by current limiting d Axial components, This is the GFL-VSC line inductor.

[0057] For GFM-VSC, its output active and reactive power can be obtained from complex power calculations: (10) (11) In the formula: The active (reactive) power output of the GFM-VSC when current limiting is not triggered; This refers to the active (reactive) synchronization item of the power grid when GFM-VSC does not trigger current limiting; This refers to the active (reactive) coupling term when GFM-VSC does not trigger current limiting; This is an intermediate computational quantity, and its value is... , for Phase angle.

[0058] Substituting equation (10) into equation (2), we can derive the simplified GFM-VSC synchronous machine model with reduced coupling effects: (12) In the formula: , and These are the power angle of GFM-VSC, the first derivative of the power angle of GFM-VSC, and the second derivative of the power angle of GFM-VSC, respectively. and These are defined as the equivalent mechanical power and equivalent output power of the GFM-VSC when the current limiting is not triggered, respectively. The equivalent mechanical power includes the influence of the GFL-VSC coupling term. This is the reference value for the active (reactive) power of the GFM-VSC when current limiting is not triggered.

[0059] After the GFM-VSC triggers rate limiting, for the GFL-VSC, by Figure 6 In section (b), based on the superposition theorem, the GFL-VSC terminal voltage phasor can be derived similarly. q Axis component expression: (13) In the formula: For the GFL-VSC terminal voltage phasor after triggering current limiting for GFM-VSC q Axis component expressions; For computational quantities, its value , for The phase angle; The current saturation phase angle for GFM-VSC; The phase angle of the GFL-VSC voltage; , and This refers to the analysis quantity after GFM-VSC triggers current limiting, where The voltage drop term is generated by the interaction between the GFL-VSC's self-injected current and the line impedance, and is defined as the self-impedance voltage drop term. This term is generated by the coupling between GFL-VSC and GFM-VSC through the transmission network and is defined as the coupling impedance voltage drop term. The term reflecting the impact of the power grid on the terminal voltage of the GFL-VSC is defined as the power grid voltage coupling term.

[0060] Substituting equation (13) into equation (1), we can derive a synchronous-like model characterizing the dynamics of GFL-VSC: (14) In the formula: and The equivalent inertia coefficient and equivalent damping coefficient of the GFL-VSC after triggering current limiting in the GFM-VSC; and These represent the equivalent mechanical power and equivalent output power of the GFL-VSC after the GFM-VSC triggers current limiting, but essentially they are still the line impedance voltage drop and the grid voltage. q Axial components; D ML2 The equivalent cross-damping coefficient of GFL-VSC after current limiting is triggered by GFM-VSC; After triggering current limiting for GFM-VSC, the phasor of the GFL-VSC inductor current d Axial components.

[0061] For GFM-VSC, its terminal voltage can be obtained by the superposition theorem: (15) In the formula: This is the equivalent impedance value of the power grid. The equivalent impedance angle of the power grid; Similarly, its output active power can be calculated from complex power: (16) In the formula: The active power output is triggered by the GFM-VSC current limiting. For the active power synchronization item of the power grid after GFM-VSC triggers current limiting; For active power coupling terms after GFM-VSC triggers current limiting; For computational quantities, its value , for Phase angle.

[0062] Substituting equation (16) into equation (2), we can derive the simplified GFM-VSC synchronous machine model with reduced coupling effects: (17) In the formula: and These can be defined as the equivalent mechanical power and equivalent output power of GFL-VSC, respectively, where the equivalent mechanical power includes the influence of GFL-VSC coupling terms; This is the active power reference value when the GFM-VSC does not trigger current limiting.

[0063] Combining equations (1)~(3) and (10)~(16) can construct Figure 7 The transient analysis model of the hybrid system shown is presented under two conditions: no current limiting is triggered and current limiting is triggered by the GFM-VSC. Figure 7 In the case where GFM-VSC does not trigger current limiting, the size of the coupling term is... I L , δ M , δ L , φ L Related to; after current limiting is triggered by GFM-VSC, the size of the coupling term is related to I L , I M , δ M , δ L , φ L , φ M Related to, among them φ M It represents a new degree of freedom for control, achieved by rationally selecting the saturation current phase angle. φ M The appropriate values ​​can effectively improve the transient stability of the system. Analysis of equations (9), (12), (14), and (17) shows that regardless of whether the GFM-VSC triggers current limiting, the connection of the GFL-VSC introduces a power coupling term, causing a change in the equivalent mechanical power of the GFM-VSC, thus affecting its power balance characteristics. Simultaneously, the connection of the GFM-VSC also introduces a voltage coupling term, causing a change in the equivalent mechanical power of the GFL-VSC, thus affecting its voltage balance characteristics. Therefore, further detailed analysis of the specific impact of converter parameters on the transient stability of the hybrid system is needed to provide parameter design schemes for improving the transient stability of the hybrid system.

[0064] S2. Analyze the impact of converter control parameters on system transient stability based on the phase plane method; A drop in grid voltage will disrupt the power balance characteristics of the GFM-VSC and the voltage balance characteristics of the GFL-VSC. Their interaction is influenced not only by the current injection method of the GFL-VSC and the power control mode of the GFM-VSC, but also by whether the GFM-VSC triggers current limiting and the setting of the saturation current phase angle. This paper analyzes the two cases: GFM-VSC not triggering and current limiting being triggered. Since this paper primarily focuses on the transient stability of the converter during a fault, for ease of analysis, it is assumed that the converters were stable before the fault, the fault duration was relatively long, and the system tended to stabilize when a stable equilibrium point existed during the fault. Specific system parameters are shown in Table 1, where the grid parameters are those of a weak grid.

[0065] To focus on the main issues, the following settings are made: 1) The converters were stable before the fault, and the fault lasted for a long time. During the fault, the converters tended to stabilize when there was a stable equilibrium point.

[0066] 2) When adjusting the converter parameters during a fault, the other parameters remain unchanged. The specific circuit parameters are shown in Table 2.

[0067] Table 2 Main Parameters

[0068] S3. Determine the optimal active power reference value and saturation current phase angle of the grid-type converter during the fault period based on the analysis results; Based on the established synchronous machine models of GFM-VSC and GFL-VSC, it is known that coupling terms alter the equivalent mechanical power of both types of converters, thereby affecting the transient stability of the hybrid system. Therefore, this study first analyzes the impact of changes in the equivalent mechanical power of the converters after a fault on the system's transient stability, and then explores the influence of the GFL-VSC output current and the GFM-VSC power reference value on the equivalent mechanical power, thereby revealing the law governing the effect of changes in these parameters on the system's transient stability.

[0069] like Figure 8 The virtual power angle curves for each converter under different mechanical power are shown. P m,0 The equivalent mechanical power of the converter before the fault. P m,F The equivalent mechanical power of the converter during the fault period. P m,b This is the mechanical power that marks the boundary between acceleration and deceleration after a fault. At this point, the virtual power angle remains unchanged before and after the fault, and the theoretical acceleration area is minimized; this is defined as the optimal mechanical power. Figure 8 It can be seen that when P m,FAs the value increases, the acceleration area of ​​the system increases, the maximum deceleration area decreases, the equilibrium point during the fault shifts to the right and away from the initial equilibrium point, and the transient stability of the system gradually decreases. P m,F When a certain critical value is exceeded, the system will no longer have a stable equilibrium point, and the fault must be promptly removed to maintain system stability. P m,F When the area decreases, the acceleration area of ​​the system decreases and the maximum deceleration area increases, but when... P m,F When it is less than a certain critical value ( P m,F < P m,b The system equilibrium point will shift to the left and deviate from the initial equilibrium point before the fault, which is detrimental to the transient stability of the hybrid system.

[0070] Phase plane diagrams of the hybrid system under different power reference values ​​of GFM-VSC are as follows: Figure 9 As shown. By Figure 9 It can be observed that adjusting the active power reference value of GFM-VSC during a fault has a significant impact on system stability: when the active power reference value of GFM-VSC increases from 0.5 pu to 0.6 pu, the system synchronously becomes unstable; while when its active power reference value decreases from 0.2 pu to 0 pu, the post-fault equilibrium points of both GFM-VSC and GFL-VSC deviate from their initial equilibrium points. Simultaneously, changes in the reactive power reference value of GFM-VSC also affect system stability: when the reactive power reference value of GFM-VSC decreases from 0 to -0.25 pu, the equilibrium points of each converter shift to the right, and system stability decreases; when the reactive power reference value of GFM-VSC increases from 0 to 0.75 pu, the equilibrium points of each converter shift to the left, and the stability of the hybrid system first increases and then decreases, and then... When the value is 0.75 pu, the post-fault equilibrium points of both GFM-VSC and GFL-VSC deviate from the initial equilibrium points.

[0071] Analysis based on equations (9) and (12) shows that increasing the active power reference value and decreasing the reactive power reference value of GFM-VSC during a fault will lead to changes in the equivalent mechanical power of GFL-VSC and GFM-VSC. P m,L1 and P m,M1Increasing the power reference value shifts the balance point of each converter to the right and worsens the transient stability of the hybrid system. Similarly, decreasing the active power reference value and increasing the reactive power reference value of the GFM-VSC during a fault will reduce the equivalent mechanical power of the GFL-VSC and GFM-VSC, causing the balance point of each converter to shift to the left and the transient stability of the hybrid system to first strengthen and then weaken. Furthermore, there exists an optimal power reference value ratio that can keep the virtual power angle value of either the GFM-VSC or GFL-VSC unchanged before and after a fault. Considering the national standard requirements for reactive current during LVRT, the virtual power angle value of the GFM-VSC can be kept unchanged before and after a fault by adjusting the active power reference value; this active power reference value is defined as the optimal active power reference value.

[0072] The impact of GFL-VSC output current on hybrid systems The phase plane diagram of the hybrid system of GFL-VSC under different output currents is as follows: Figure 10 As shown. By Figure 10 It can be observed that adjusting the active current of the GFL-VSC during a fault has a significant impact on system stability: when the active current output by the GFL-VSC increases from 0.8 pu to 1 p.u., the system synchronously becomes unstable; while when its active current decreases from 0.2 pu to 0, the post-fault equilibrium points of the GFM-VSC and GFL-VSC deviate from their initial equilibrium points. Simultaneously, changes in the reactive current of the GFL-VSC also affect system stability: the GFL-VSC absorbs reactive current ( I q,L When the reactive power of the converter increases from 0 to 1 p.u., the balance point of each converter shifts to the right, and the stability of the hybrid system decreases; the reactive power output of the GFL-VSC ( I q,L When <0) increases from 0 to 1 p.u., the system stability first increases and then decreases, and then... I q,L When the value is -1 p.u., the post-fault equilibrium point of GFM-VSC and GFL-VSC deviates from the initial equilibrium point.

[0073] Analysis based on equations (9) and (12) shows that increasing the active current output of GFL-VSC and decreasing the reactive current output of GFL-VSC during a fault will lead to an increase in the equivalent mechanical power of GFM-VSC and GFL-VSC. P m,L1 and P m,M1Increasing the current will shift the balance point of each converter to the right and worsen the transient stability of the hybrid system. Similarly, reducing the active current output of GFL-VSC and increasing the reactive current output of GFL-VSC during a fault will reduce the equivalent mechanical power of GFM-VSC and GFL-VSC, shift the balance point of each converter to the left, and the transient stability of the hybrid system will first become stronger and then weaker. Moreover, there are multiple sets of optimal current ratios that can keep the virtual power angle value of GFL-VSC or GFM-VSC unchanged before and after the fault.

[0074] After GFM-VSC triggers current limiting, the external characteristics of GFL-VSC remain unchanged and can still be used. Figure 8 Analysis is required, but the external characteristics of the GFM-VSC change, necessitating a separate analysis of its virtual power angle curve.

[0075] The Influence of GFM-VSC Saturation Current Phase Angle on Hybrid Systems When the GFM-VSC triggers current limiting, its transient stability can be improved by adjusting the saturation current phase angle. As analyzed in Section 1, after triggering current limiting, to meet the low-voltage ride-through standard requirements, the active power reference value of the GFM-VSC during the fault period should be reduced accordingly. Assuming the disturbance is large enough that it triggers current limiting instantaneously, the equivalent mechanical power of the GFM-VSC will change abruptly upon triggering current limiting. For example... Figure 11 As shown, P m,0 The equivalent mechanical power of GFM-VSC before the fault. P m,F This represents the equivalent mechanical power of the GFM-VSC after a fault. From... Figure 11 It can be seen that as the absolute value of the saturation current phase angle increases, the GFM-VSC saturation virtual power angle curve will shift to the right, its deceleration area will decrease, the system's transient stability will first increase and then decrease, and there exists an optimal saturation current phase angle. φ M,b This ensures that the virtual power angle value remains unchanged before and after the fault. At this point, the theoretical acceleration area of ​​the converter is minimized, and the transient synchronization stability of the entire hybrid system reaches a high level.

[0076] The phase plane diagrams of the hybrid system with different saturation current phase angles under fault conditions using GFM-VSC are as follows: Figure 12 As shown. By Figure 12 It can be observed that as the phase angle of the saturation current of the GFM-VSC increases... φ M As the concentration decreases, the transient stability of GFM-VSC and GFL-VSC initially increases and then decreases. φ MWhen the fault equilibrium point of GFM-VSC deviates from the initial equilibrium point at -π / 2, it can be seen from the analysis of equations (14) and (17) that although adjusting the saturation current phase angle will not change the fault equilibrium point of GFM-VSC, a suitable saturation current phase angle can reduce the power angle deviation of GFM-VSC before and after the fault, accelerate the stabilization process of the hybrid system, and thus effectively improve the transient stability of the hybrid system during the fault.

[0077] GFM-VSC adopts q Shaft-priority current limiting can effectively reduce the power angle deviation before and after a fault and improve the system stability margin, therefore this paper selects... q The impact of axis-priority current limiting on the output current of GFL-VSC is analyzed, and the virtual power angle curve of GFL-VSC is compared with that of GFL-VSC. Figure 8 Similar. For example... Figure 13 Phase plane diagrams of the hybrid system under different GFM-VSC saturation current phase angles when current limiting is triggered. Figure 13 It can be observed that adjusting the active current of the GFL-VSC during a fault has a significant impact on system stability: when the active current output by the GFL-VSC increases from 0.2 pu to 0.3 pu, the system synchronously becomes unstable; when its active current output decreases from 0.2 pu to 0.1 pu, the fault equilibrium point of both the GFM-VSC and the GFL-VSC deviates from the initial equilibrium point. Simultaneously, changes in the reactive current of the GFL-VSC also affect system stability: the GFL-VSC absorbs reactive current (…). I q,L When the reactive current (>0) increases from 0 to 0.3 pu, the system stability decreases; the GFL-VSC output reactive current ( I q,L When the value of <0) increases from 0 to 0.9 pu, the system stability first increases and then decreases, and then... I q,L When the value is -0.9 pu, the fault equilibrium point of GFM-VSC and GFL-VSC deviates from the initial equilibrium point.

[0078] Analysis of equations (12) and (13) shows that increasing the active current output of GFL-VSC or decreasing its reactive current output during a fault will increase the equivalent mechanical power of GFM-VSC and GFL-VSC, leading to a decrease in the transient stability of the hybrid system. Conversely, decreasing the active current output of GFL-VSC or increasing its reactive current output during a fault will decrease the equivalent mechanical power of GFM-VSC and GFL-VSC, resulting in a first increase and then a decrease in the transient stability of the hybrid system. Furthermore, there exists an optimal current ratio for GFL-VSC that can keep the virtual power angle value unchanged before and after the fault. In summary, this paper uses the phase plane method to systematically analyze the transient response characteristics of the hybrid system under a grid voltage sag. This method effectively reveals the influence mechanism of key parameters such as the power reference value of GFM-VSC, the output current of GFL-VSC, and the phase angle of the saturated current of GFM-VSC on system stability. The analysis results show that regardless of whether GFM-VSC triggers current limiting, adjusting the converter output can keep the virtual power angle unchanged before and after the fault, at which point the system exhibits optimal transient stability. Furthermore, this paper also obtains the stable operating boundaries of the hybrid system under different operating conditions through systematic parameter scanning, and the results are as follows: Figure 22 As shown.

[0079] S4. Design and implement an adaptive fault ride-through control strategy based on the optimal parameters.

[0080] Transient stability analysis of the hybrid system reveals that adjusting the active power reference value to approach the optimal value when the GFM-VSC is not triggered by current limiting, and adjusting the saturation current phase angle to approach the optimal saturation current phase angle after the GFM-VSC triggers current limiting, minimizes the theoretical acceleration area of ​​the GFM-VSC. In this case, the power angle balance point under GFM-VSC fault conditions will be as close as possible to the initial power angle balance point, effectively improving the transient stability of the hybrid system. Based on this idea, this paper proposes an adaptive fault ride-through control strategy for the GFM-VSC, the control block diagram of which is shown below. Figure 11 As shown.

[0081] Figure 11 The fault-memory module is used to collect the power angle of the GFM-VSC at the moment of the fault; the current saturation limiting module uses effective value limiting with additional phase angle mode switching to ensure that the GFM-VSC current is always within the allowable range; the fault judgment and mode selection module is used for fault identification, and when the grid connection point voltage of the GFM-VSC is less than 0.9pu, its power reference value always meets the requirements. Figure 4 Constraints, and through U C-V To determine whether the GFM-VSC has reached its maximum reactive current, the fault ride-through control strategy (F1 / F2) is switched accordingly. U M exist U C-VWhen the value is between ~0.9, the GFM-VSC uses adaptive active power reference control (F1). U M In 0~ U C-V At this time, GFM-VSC adopts adaptive saturation current phase angle control (F2); the control strategies for the two control modes are as follows: 1) Adaptive Active Power Reference Value Control To make the fault-balanced power angle approach the power angle before the fault, refer to equation (10) to obtain the reference value of active power after the fault: (18) In the formula, This is a reference value for active power after the fault. and The voltage at the GFM-VSC terminal after the fault and the voltage of the mains grid after the fault; and The voltage at the GFM-VSC terminal before the fault and the voltage of the mains grid before the fault are given. This is the initial power reference value for the grid-type converter. This is a power coupling term.

[0082] Considering the power coupling term of GFL-VSC To mitigate the impact of [the situation], and to obtain the optimal active power reference value, the following approach is adopted: Figure 14 The control block diagram shown illustrates the process when current limiting is not triggered. Quickly adjust the active power reference value in response to voltage changes, and adjust the power angle during faults. Power angle before fault The influence of coupling terms is eliminated by comparison, thereby obtaining the optimal active power reference value, so that the fault power angle balance point of GFM-VSC approaches the initial power angle balance point, effectively suppressing oscillation.

[0083] When the GFM-VSC triggers current limiting, as analyzed by the transient model in Section 3, there exists an optimal saturation current phase angle that keeps the power angle unchanged before and after the fault. This optimal saturation current phase angle is jointly determined by the equivalent mechanical power of the GFM-VSC, the power angle equilibrium point before the fault, and the virtual power angle curve of the GFM-VSC after the fault; its value is difficult to directly tune. To obtain the optimal saturation current phase angle, the control block diagram is designed as follows: Figure 14 As shown: Using q The axis-priority current limiting with power angle compensation stage acquires the power angle at the moment of low-voltage ride-through after current limiting is triggered. Power angle during fault The saturation current phase angle is adjusted by comparison to obtain the optimal saturation current phase angle, so that the fault power angle equilibrium point approaches the initial power angle equilibrium point, effectively suppressing oscillation.

[0084] The final power angle response process of GFM-VSC is shown in the figure. By using adaptive active power reference value control and adaptive saturation phase angle control, the power angle balance point during GFM-VSC faults is made as close as possible to the initial power angle balance point, effectively improving the transient stability of the hybrid system.

[0085] Simulation verification To verify the correctness of the theoretical analysis and control strategy presented in this paper, a system was built in MATLAB / Simulink as follows: Figure 1 The main simulation parameters of the hybrid system grid connection simulation model shown are listed in Table 2. Figure 16 Simulation results for a hybrid system under different power reference values ​​for GFM-VSC are presented. The simulation conditions are as follows: initially, each converter in the hybrid system outputs active power at 50% of its rated current; the grid voltage drops to 0.6 pu after 0.4 seconds. Figure 16 As can be seen, increasing the active power reference value and decreasing the reactive power reference value of the GFM-VSC during a fault will worsen the transient stability of the hybrid system: when its active power reference value increases from 0.8 pu to 1 p.u., the hybrid system becomes transiently synchronously unstable; when the active power reference value of the GFM-VSC is decreased and the reactive power reference value of the GFM-VSC is increased during a fault, the transient stability of the hybrid system will first become stronger and then weaker, and there is an optimal power reference value ratio of the GFM-VSC that can keep its virtual power angle value unchanged before and after the fault.

[0086] Figure 17 The simulation results of the hybrid system of GFL-VSC under different output currents are shown, and the simulation conditions are set as follows: Figure 16 Same. From Figure 17 It can be seen that increasing the active current output of the GFL-VSC and decreasing the reactive current output of the GFL-VSC during a fault will worsen the transient stability of the hybrid system: when its output current ( I d,L , I q,L When )=(1,0)pu, the system synchronously becomes unstable; during the fault period, when the active current output of GFL-VSC is reduced and the reactive current output of GFL-VSC is increased, the transient stability of the hybrid system will first become stronger and then weaker, and there is an optimal current ratio of GFL-VSC that can keep the virtual power angle value unchanged before and after the fault.

[0087] Figure 18 The simulation results for the GFM-VSC hybrid system under different saturation current phase angles are presented. The simulation conditions are as follows: initially, each converter in the hybrid system outputs active power at 50% of its rated current, and the grid voltage drops to 0.1 pu after 0.4 s. Figure 18 As can be seen, with the phase angle of the saturation current of the GFM-VSC... φ MAs the value decreases, the transient stability of GFM-VSC and GFL-VSC first increases and then decreases. φ M When the value is -5π / 8, the fault equilibrium point of the GFM-VSC deviates from the initial equilibrium point. Figure 18 As can be seen in (b), the adjustment φ M Although it will not change the fault equilibrium point of GFL-VSC, the appropriate saturation current phase angle can reduce the power angle deviation of GFL-VSC before and after the fault, accelerate the stabilization process of the hybrid system, and thus effectively improve the transient stability of the hybrid system during the fault.

[0088] Figure 19 Simulation results of the hybrid system of GFL-VSC under different output currents, simulation condition settings and Figure 19 Same. From Figure 19 It can be seen that increasing the active current output of the GFL-VSC and decreasing the reactive current output of the GFL-VSC during a fault will worsen the transient stability of the hybrid system: when its output current ( I d,L , I q,L When )=(0.5,0)pu, the system synchronously becomes unstable; during the fault period, when the active current output of GFL-VSC is reduced and the reactive current output of GFL-VSC is increased, the transient stability of the hybrid system will first become stronger and then weaker, and there exists an optimal current ratio of GFL-VSC that can keep the virtual power angle value unchanged before and after the fault.

[0089] To verify the superiority of the proposed improved control strategy compared to the traditional GFM-VSC control strategy, a time-domain simulation of the hybrid system was performed using MATLAB. The simulation conditions are as follows: initially, each converter in the hybrid system outputs active power at 50% of its rated current. After 0.4 seconds, the grid voltage drops to 0.6 pu, at which point the GFM-VSC does not trigger current limiting. Figure 20 Simulation results are presented under both traditional and improved control strategies. Figure 20 (a) shows the changes in the power angle under the traditional VSG control strategy and the improved control strategy. After a fault, the power angle of the GFM-VSC will increase due to the voltage sag and then stabilize at a new equilibrium point under the traditional VSG control strategy. However, the improved control proposed in this paper can adaptively adjust the active power reference value to keep the power angle unchanged before and after the fault. It can be seen that, compared with the traditional VSG control strategy, the improved control strategy proposed in this paper can adaptively adjust the active power reference value of the GFM-VSC after a fault, maintain the constant power angle of the GFM-VSC before and after the fault, and greatly improve the transient stability of the hybrid system.

[0090] To verify the superiority of the adaptive saturated current phase angle control strategy designed in this paper in improving the transient stability of the system, a time-domain simulation of the hybrid system was performed using MATLAB. The simulation conditions are as follows: the hybrid system initially operates in a steady state, and the grid voltage drops to 0.3 pu at 0.4 s, at which point the GFM-VSC triggers current limiting. Figure 21 Shown in d Axis priority current limiting q Simulation results under priority axis current limiting and improved current limiting control strategies.

[0091] Figure 21 Figure (a) shows the power angle offset of GFM-VSC under different current limiting methods, compared with the traditional d Axis priority current limiting and q The proposed saturated current phase angle adaptive control strategy can adaptively adjust the phase angle of the GFM-VSC saturated current after a fault, quickly maintain the stability of the GFM-VSC power angle, shorten the GFL-VSC stabilization time, and effectively improve the transient stability of the hybrid system during faults.

[0092] In addition, combined Figures 23-26 Comparative analysis reveals that when GFM-VSC does not trigger current limiting, the initial stable power angle of a weak grid is higher than that of a strong grid, and the weaker the grid, the larger the initial power angle. This also makes it easier for a weak grid to exceed the critical power angle and become unstable under large voltage sag disturbances. Nevertheless, the parameter influence laws and control optimization directions revealed in this paper remain consistent under different grid strengths, fully verifying the universality of the theoretical analysis.

[0093] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0094] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0095] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0096] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0097] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting, characterized in that, Includes the following steps: S1. Establish a transient analysis model for a hybrid system of grid-connected converters and grid-connected converters, taking into account the current limiting circuit of the grid-connected converter. S2. Analyze the impact of converter control parameters on system transient stability based on the phase plane method; S3. Determine the optimal active power reference value and saturation current phase angle of the grid-type converter during the fault period based on the analysis results; S4. Design and implement an adaptive fault ride-through control strategy based on the optimal parameters.

2. The method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting as described in claim 1, characterized in that, The specific method for establishing the transient analysis model in S1 is as follows: System mathematical models for the grid-type converter under two operating conditions—untriggered current limiting and triggered current limiting—are established respectively. These models include a quasi-synchronous machine model for the grid-connected converter and a synchronous machine model for the grid-type converter. The active-frequency control equation and reactive-voltage control equation for the grid-type converter are expressed as follows: In the formula, The virtual inertia of the grid-type converter. For the power angle of the grid-type converter, This is the active power reference value for grid-type converters. This refers to the actual output active power of the grid-type converter. The angular frequency of the power grid. The damping coefficient of the grid-type converter. This is the reactive power reference value for grid-type converters. This represents the actual reactive power of the grid-connected converter. This is the voltage reference amplitude for the grid-type converter. The initial voltage value for the grid-type converter. This is the reactive power loop droop factor for a grid-type converter.

3. The method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting as described in claim 1, characterized in that, The specific method for analyzing the influence of converter control parameters based on the phase plane method in S2 is as follows: analyze the influence of the active power reference value, reactive power reference value, and output active and reactive current of the grid-type converter on the transient stability of the system, and quantify the effect of parameter changes on the power angle balance point through the phase plane diagram; among them, the equivalent mechanical power and equivalent output power of the grid-type converter are used to evaluate transient stability, and the calculation of the equivalent mechanical power involves the coupling terms of the grid-type converter.

4. The method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting as described in claim 3, characterized in that, The specific method for determining the optimal active power reference value and saturation current phase angle in S3 is as follows: The parameter value that minimizes the power angle deviation before and after the fault is found using the phase plane method; the optimal active power reference value is dynamically calculated based on the voltage ratio and power coupling term before and after the fault, and the calculation formula is: In the formula, This is a reference value for active power after the fault. and The voltage at the GFM-VSC terminal after the fault and the voltage of the mains grid after the fault; and The voltage at the GFM-VSC terminal before the fault and the voltage of the mains grid before the fault are given. This is the initial power reference value for the grid-type converter. This is a power coupling term.

5. The method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting as described in claim 1, characterized in that, The adaptive fault ride-through control strategy in S4 includes two modes: when the grid-type converter does not trigger current limiting, adaptive active power reference value control is used; when the grid-type converter triggers current limiting, adaptive saturated current phase angle control is used; wherein, the current limiting expression of the grid-type converter is: In the formula, This is the current reference value for the grid-type converter after current limiting. The phase angle of the saturation current. This is the maximum allowable current for a grid-type converter. This is the initial current reference value for the grid-type converter.

6. The method for transient stability analysis and fault ride-through control of a hybrid system considering current limiting according to claim 5, characterized in that, The specific method of the adaptive saturated current phase angle control is as follows: A q-axis priority current limiting and power angle compensation circuit is used to adjust the saturated current phase angle based on the deviation between the power angle acquired at the moment of the fault and the current power angle, thereby reducing power angle oscillation; the q-axis priority current limiting corresponds to the saturated current phase angle. .

Images