Network configuration type vsc transient stability analysis method and system considering inner loop dynamic influence

Abstract

The application discloses a network-constructing type VSC transient stability analysis method and system considering internal ring dynamic influence, and comprises the following steps: determining the control system of GFM-VSC, determining active power and virtual power angle based on virtual synchronous power outer ring control; determining port node voltage phase and internal potential amplitude based on the active power and virtual power angle; determining the output current amplitude of GFM-VSC based on the internal potential amplitude and virtual power angle; determining whether the saturation link of GFM-VSC is triggered based on the internal potential amplitude and output current amplitude, and determining the saturation link type when it is determined that the saturation link is triggered; and analyzing the transient stability according to the saturation link type.

Description

Technical Field

[0001] This invention relates to the field of grid-type converter technology, and more specifically, to a transient stability analysis method and system for grid-type VSC that takes into account the dynamic effects of the inner loop. Background Technology

[0002] In recent years, to further explore the potential of power electronic equipment to support the safe and stable operation of new power systems, grid-forming (GFM) control technology, originating from the microgrid field, has once again attracted widespread attention from academia and industry. The core components of grid-forming control technology include two parts: power outer-loop control and inner-loop control. Power outer-loop control aims to autonomously generate internal potential amplitude and phase references, providing a voltage vector reference for inner-loop control. Currently, various power outer-loop control methods have been proposed, including droop control, virtual synchronous machine control, matching control, and virtual oscillator control, to adapt to the differentiated needs of different equipment carriers or application scenarios. Furthermore, regarding the time scale of the power outer loop, numerous studies have explored in depth the small-disturbance oscillation characteristics, transient stability mechanisms, and system strength support characteristics of grid-connected systems with grid-forming equipment. Overall, research on power outer-loop control is relatively mature.

[0003] Currently, research on the transient stability mechanism of GFM-VSC considering the dynamic effects of the voltage and current inner loop still has limitations. Therefore, a transient stability analysis method for GFM-VSC that takes into account the dynamics of the voltage and current inner loop is needed. Summary of the Invention

[0004] This invention proposes a transient stability analysis method and system for grid-type VSC that takes into account the dynamic effects of the inner loop, in order to solve the problem of how to analyze the potential impact of triggered saturation on grid-type converters during the voltage-current inner loop regulation process.

[0005] To address the aforementioned problems, according to one aspect of the present invention, a transient stability analysis method for a network-type VSC considering the dynamic influence of the inner loop is provided, the method comprising: The control system of GFM-VSC is determined, and the active power and virtual power angle are determined based on the virtual synchronous power outer loop control. The phase of the port node voltage and the amplitude of the internal potential are determined based on the active power and the virtual power angle. The output current amplitude of the GFM-VSC is determined based on the internal potential amplitude and the virtual power angle. Based on the internal potential amplitude and the output current amplitude, determine whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, determine the type of saturation circuit. Transient stability analysis is performed based on the type of saturated process.

[0006] Preferably, the determination of active power and virtual power angle based on virtual synchronous power outer loop control includes: , Where P is the active power; δ This is a virtual work angle; P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

[0007] Preferably, determining the port node voltage phase and internal potential amplitude based on the active power and virtual power angle includes: , , in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0008] Preferably, determining the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle includes: , Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0009] Preferably, based on the internal potential amplitude and the output current amplitude, it is determined whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, the type of saturation circuit is determined, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

[0010] Preferably, the transient stability analysis based on the type of saturated stage includes: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value. I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential...E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which, i dref , i d These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

[0011] According to another aspect of the present invention, a network-type VSC transient stability analysis system considering the dynamic effects of the inner loop is provided, the system comprising: The first calculation unit is used to determine the control system of GFM-VSC, and determines the active power and virtual power angle based on the virtual synchronous power outer loop control. The second calculation unit is used to determine the voltage phase and internal potential amplitude of the port node based on the active power and virtual power angle. The third calculation unit is used to determine the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle. The judgment unit is used to determine whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and to determine the type of saturation circuit when it is determined that a saturation circuit has been triggered. The stability analysis unit is used to analyze transient stability based on the type of saturated element.

[0012] Preferably, the first calculation unit determines the active power and virtual power angle based on the virtual synchronous power outer loop control, including: , Where P is the active power; δ This is a virtual work angle; P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

[0013] Preferably, the second calculation unit determines the port node voltage phase and internal potential amplitude based on the active power and virtual power angle, including: , , in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0014] Preferably, the third calculation unit determines the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle, including: , Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0015] Preferably, the determination unit determines whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and determines the type of saturation circuit when it is determined that a saturation circuit has been triggered, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

[0016] Preferably, the stability analysis unit performs transient stability analysis based on the type of saturated element, including: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value.I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which, i dref , i d These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

[0017] This invention provides a transient stability analysis method and system for network-type VSCs that considers the dynamic effects of the inner loop. The method includes: determining the control system of the GFM-VSC; determining the active power and virtual power angle based on the virtual synchronous power outer loop control; determining the voltage phase and internal potential amplitude of the port nodes based on the active power and virtual power angle; determining the output current amplitude of the GFM-VSC based on the internal potential amplitude and virtual power angle; determining whether the GFM-VSC has triggered a saturation stage based on the internal potential amplitude and output current amplitude, and determining the type of saturation stage when it is determined; and performing transient stability analysis based on the type of saturation stage. This invention reveals the current and internal potential saturation instability mechanism under the dynamic effects of the inner loop, overcoming the shortcomings of existing studies that only consider a single current-limiting factor, leading to overly optimistic transient stability assessment results. It can efficiently and accurately perform transient stability analysis on network-type VSCs. Attached Figure Description

[0018] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 A flowchart of a network-type VSC transient stability analysis method 100 considering the dynamic effects of the inner loop according to an embodiment of the present invention; Figure 2 The network-type VSC system topology and control strategy according to an embodiment of the present invention; Figure 3 A simplified circuit diagram of a GFM-VSC unit connected to an equivalent power grid according to an embodiment of the present invention; Figure 4 This is a diagram showing the voltage vector relationships during the current-limited GFM-VSC disturbance process according to an embodiment of the present invention. Figure 5 The diagram shows the voltage vector relationships during the GFM-VSC disturbance process under internal potential limiting according to an embodiment of the present invention. Figure 6 This represents the unintended stable equilibrium point of the different current limiting strategies according to embodiments of the present invention; Figure 7 This is the unintended stable equilibrium point under the internal potential limiting according to the embodiment of the present invention; Figure 8 This refers to the transient output characteristics of GFM-VSC under the untriggered saturation circuit according to an embodiment of the present invention; Figure 9 The transient output characteristics (q-axis) of GFM-VSC under trigger current limiting according to an embodiment of the present invention. Figure 10 This describes the transient output characteristics of the GFM-VSC under the trigger internal potential limiting according to an embodiment of the present invention. Figure 11 This is a schematic diagram of the structure of a network-type VSC transient stability analysis system 1100 that takes into account the dynamic effects of the inner loop according to an embodiment of the present invention. Detailed Implementation

[0019] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0020] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0021] Existing research mainly focuses on fault ride-through characteristics, transient current limiting effects, and their impact on the power outer loop-dominated transient stability mechanism, without fully exploring the potential impact of the voltage-current inner loop regulation process and its triggering saturation on grid-type converters. Therefore, to address this issue, this invention proposes a GFM-VSC transient stability analysis method and system that considers the dynamics of the voltage and current inner loop.

[0022] Figure 1 This is a flowchart of a network-type VSC transient stability analysis method 100 considering the dynamic effects of the inner loop according to an embodiment of the present invention. Figure 1 As shown, the transient stability analysis method for network-type VSCs considering the dynamic influence of the inner loop provided by the embodiments of the present invention reveals the current and internal potential saturation instability mechanism under the dynamic influence of the inner loop. This overcomes the shortcomings of existing studies that only consider a single current-limiting factor, leading to overly optimistic transient stability assessment results. It can efficiently and accurately perform transient stability analysis on network-type VSCs. The transient stability analysis method 100 for network-type VSCs considering the dynamic influence of the inner loop provided by the embodiments of the present invention starts from step 101. In step 101, the control system of the GFM-VSC is determined, and the active power and virtual power angle are determined based on the virtual synchronous power outer loop control.

[0023] Preferably, the determination of active power and virtual power angle based on virtual synchronous power outer loop control includes: , Where P is the active power; δ This is a virtual work angle; PN These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

[0024] In step 102, the voltage phase and internal potential amplitude of the port node are determined based on the active power and the virtual power angle.

[0025] Preferably, determining the port node voltage phase and internal potential amplitude based on the active power and virtual power angle includes: , , in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0026] In step 103, the output current amplitude of the GFM-VSC is determined based on the internal potential amplitude and the virtual power angle.

[0027] Preferably, determining the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle includes: , Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0028] In this invention, the control system of GFM-VSC is first determined, and the virtual synchronous power outer loop control is as follows, from which the output active power can be obtained. PWith virtual power angle δ for: , In the formula, P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle (i.e., the phase of the internal potential) and the virtual angular frequency, respectively.

[0029] Then, the port node voltage phase is obtained based on the circuit relationship of the GFM-VSC grid-connected system. θ for: (2) In the formula, U g This refers to the voltage amplitude at the grid-side power supply node. U VSC and θ This refers to the output node voltage amplitude and phase; X L For grid-connected line reactance.

[0030] Furthermore, the amplitude of the internal potential is derived. E for: (3) In the formula, X F To equip with filter reactors.

[0031] Then, the output current amplitude of the GFM-VSC is obtained as follows: (4) In step 104, based on the internal potential amplitude and the output current amplitude, it is determined whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, the type of saturation circuit is determined.

[0032] Preferably, based on the internal potential amplitude and the output current amplitude, it is determined whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, the type of saturation circuit is determined, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

[0033] In step 105, transient stability is analyzed based on the type of saturated element.

[0034] Preferably, the transient stability analysis based on the type of saturated stage includes: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value. I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which... i dref , id These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

[0035] In this invention, during the process of determining transient disturbance, it is necessary to determine whether the GFM-VSC triggers the saturation stage. If equation (5) is not satisfied, then the saturation stage is triggered. (5) In the formula, I max This represents the maximum output current amplitude of the GFM-VSC. E max This represents the maximum amplitude of the internal potential of the GFM-VSC.

[0036] Among them, if Then the trigger current saturation stage is determined; if This determines that the internal potential limiting circuit is triggered.

[0037] In this invention, if a current saturation stage is triggered, the transient stability dominated by current saturation is determined, as follows: 1. At the moment of recovery, U VSC Greater than U ref The voltage inner-loop integrator enters the desaturation process. However, different current limiting strategies can lead to differences in the output current phase, resulting in different equipment operating states at the moment of recovery. At the moment of disturbance clearance, if the reference value and actual value of the inner-loop voltage under the current saturation state satisfy the following relationship: (6) In the formula, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively.

[0038] At this time, the voltage inner loop control lowers the current reference value. I ref GFM-VSC can enter a desaturation process.

[0039] 2. If equation (6) is not satisfied at the moment of disturbance clearing, the negative feedback regulation mechanism of the voltage and current inner loop control fails, and the voltage inner loop control cannot lower the current reference value.I ref When the power outer loop recovers to an unintended stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting.

[0040] Among them, the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation.

[0041] In this invention, if the internal potential limiting circuit is triggered, the transient stability dominated by internal potential saturation is determined, as follows: 1. At the instant of recovery, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state satisfy the following relationship: (7) At this point, the inner current loop integrator begins to desaturate. E Gradually decrease. When E < E max At that time, GFM-VSC had exited the saturation state.

[0042] 2. If the fault is cleared instantly, it meets the following criteria: i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E Continuous saturation. When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters the saturation instability mode dominated by the internal potential.

[0043] Among them, the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value intersects with the power angle curve under the internal potential saturation state.

[0044] The following specific examples illustrate the embodiments of the present invention. In an embodiment of the present invention, taking a typical virtual synchronous VSG control strategy as an example, the specific topology and control strategy are as follows: Figure 2 As shown, where, u , i These are the port output voltage and current, respectively. P T and Q T Output the active and reactive power of the node; U ref , ω ref , δThese represent the amplitude, frequency, and phase of the outer loop output reference voltage, respectively. u ref This is the outer loop output reference voltage; e This is the internal potential.

[0045] The transient stability analysis method for network-type VSC that takes into account DC dynamic effects includes the following steps: Step 1: Determine the control system of GFM-VSC. The virtual synchronous power outer loop control is as follows: (1) In the formula, P N and Q N These are the rated active and reactive power settings, respectively. J and τ These are the virtual inertia coefficient and the reactive power regulation coefficient, respectively. K P and K Q These are the active frequency and the reactive voltage droop coefficient, respectively. D P This is the virtual damping coefficient; U N and ω N These are the rated AC voltage amplitude and frequency, respectively.

[0046] Step 2: Figure 3 A simplified circuit diagram for a single unit of grid-connected equipment connected to an equivalent power grid is presented. The phase of the port node voltage is obtained based on the circuit relationship of the GFM-VSC system connected to the grid. θ for: (2) In the formula, U g This refers to the voltage amplitude at the grid-side power supply node. U VSC and θ This refers to the output node voltage amplitude and phase; X L For grid-connected line reactance.

[0047] Furthermore, the amplitude of the internal potential is derived. E for: (3) Step 3: Calculate the output current amplitude of the GFM-VSC as follows: (4) Step 4: Determine whether the GFM-VSC triggers the saturation stage during the transient disturbance process. If it does not satisfy equation (5), then the saturation stage is triggered.

[0048] (5) In the formula, I max This represents the maximum output current amplitude of the GFM-VSC. E max This represents the maximum amplitude of the internal potential of the GFM-VSC.

[0049] Step 5: If If the current saturation stage is triggered, the transient stability dominated by current saturation is determined as follows: Step 5-1: Figure 4 This demonstrates the voltage vector relationships in a GFM-VSC grid-connected system under current-limited conditions, during steady state, fault occurrence, and instantaneous recovery. In the instantaneous recovery phase... U VSC Greater than U ref The voltage inner-loop integrator enters the desaturation process. However, different current limiting strategies can lead to differences in the output current phase, resulting in different equipment operating states at the moment of recovery. If, at the moment the disturbance is cleared, the reference and actual values ​​of the inner-loop voltage under the current-saturated state satisfy the following relationship... (6) In the formula, u d ,u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively.

[0050] At this time, the voltage inner loop control lowers the current reference value. I ref GFM-VSC can enter a desaturation process.

[0051] Step 5-2: If equation (6) is not satisfied, the negative feedback regulation mechanism of the voltage-current inner loop control fails, and the voltage inner loop control cannot lower the current reference value. I ref If the power outer loop recovers to the unintended stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting. The unintended stable equilibrium points of different current limiting strategies are as follows: Figure 5 As shown in the figure. The unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation.

[0052] Step 6: If If the internal potential limiting circuit is triggered, the transient stability dominated by internal potential saturation is determined as follows: Step 6-1: Figure 6This paper demonstrates the voltage vector relationships during the duration and recovery of a grid-connected fault in a GFM-VSC under internal potential limiting conditions. At the recovery instant, the reference and actual values ​​of the inner loop current, dominated by the internal potential saturation state, satisfy the following relationship: (7) At this point, the inner current loop integrator begins to desaturate. E Gradually decrease. When E < E max At that time, GFM-VSC had exited the saturation state.

[0053] Step 6-2: If the fault is cleared instantly, it meets the following criteria: i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E Continuous saturation. If the power outer loop recovers to the unintended stable equilibrium point under the internal potential saturation state, the GFM-VSC enters the saturation instability mode dominated by the internal potential. The unintended stable equilibrium point under internal potential limiting is as follows: Figure 7 As shown in the figure. The unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value intersects with the power angle curve under the internal potential saturation state.

[0054] Specific simulation waveforms are as follows Figure 8 , Figure 9 and Figure 10 As shown.

[0055] The Figure 8 The transient output characteristics of GFM-VSC with different control architectures under non-triggered saturation conditions are demonstrated, including simulated waveforms of grid-side voltage, port output voltage and internal potential, output current, output power, and virtual power angle. Figure 8 (a) It can be seen that during the occurrence and clearance of a grid-side fault, the GFM-VSC cannot maintain a constant internal potential due to the dynamic adjustment of the voltage and current inner loop control. During the fault persistence phase, the equipment's internal potential has reached 2.0 pu, and the equipment's output current gradually increases, even exceeding 3.0 pu.

[0056] The Figure 9 The transient output characteristics of the GFM-VSC under trigger current amplitude constraints are demonstrated, where the current limiting strategy employs a q-axis current-priority strategy. Figure 9 It can be seen that after the current limiting circuit is triggered during the fault period, the equipment current inner loop control achieves closed-loop regulation to reach a steady state, and the output current is effectively suppressed to 3.0 pu. Figure 9 In (e) and (f), the voltage inner loop remains unstable under current limiting, causing its integrator to continuously integrate. After the disturbance is cleared, the port voltage vector dominated by the current limiting mode and the reference voltage vector given by the power outer loop cannot form a negative feedback regulation mechanism to change the reference value of the current inner loop. That is, the equipment output current is locked to the limiting mode and cannot be recovered, resulting in transient instability.

[0057] The Figure 10 This demonstrates the transient output characteristics of the GFM-VSC under triggered internal potential limiting constraint. During the fault duration, after triggering internal potential limiting, the internal potential is locked at 1.5 pu, and simultaneously constrained by current limiting. Through dynamic adjustment via the current loop, the output current is limited to 3.0 pu. After the fault is cleared, although the output current of the GFM-VSC decreases, its internal potential cannot recover and remains locked at 1.5 pu. Figure 10 (f) It can be seen that at the instant the disturbance is cleared, under the constraint of internal potential limiting... d The reference value and actual value of the shaft current inner loop do not meet the negative feedback regulation conditions, therefore a deviation always exists, and continuous integration leads to internal potential saturation instability. Figure 10 As can be seen from (c) and (d), although the virtual power angle is restored to the initial state, it is attracted by the non-expected equilibrium point, and the output reactive power cannot be restored.

[0058] Figure 11 This is a schematic diagram of the structure of a network-type VSC transient stability analysis system 1100 that considers the dynamic effects of the inner loop according to an embodiment of the present invention. Figure 11 As shown, the network-type VSC transient stability analysis system 1100 considering the dynamic influence of the inner loop provided by the embodiment of the present invention includes: a first calculation unit 1101, a second calculation unit 1102, a third calculation unit 1103, a judgment unit 1104, and a stability analysis unit 1105.

[0059] Preferably, the first calculation unit 1101 is used to determine the control system of GFM-VSC and determine the active power and virtual power angle based on the virtual synchronous power outer loop control.

[0060] Preferably, the first calculation unit 1101 determines the active power and virtual power angle based on the virtual synchronous power outer loop control, including: , Where P is the active power; δ This is a virtual work angle; P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D PThis is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

[0061] Preferably, the second calculation unit 1102 is used to determine the voltage phase and internal potential amplitude of the port node based on the active power and the virtual power angle.

[0062] Preferably, the second calculation unit 1102 determines the port node voltage phase and internal potential amplitude based on the active power and virtual power angle, including: , , in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0063] Preferably, the third calculation unit 1103 is used to determine the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle.

[0064] Preferably, the third calculation unit 1103 determines the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle, including: , Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

[0065] Preferably, the judgment unit 1104 is used to determine whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and to determine the type of saturation circuit when it is determined that a saturation circuit has been triggered.

[0066] Preferably, the judgment unit 1104 determines whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and determines the type of saturation circuit when it is determined that a saturation circuit has been triggered, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

[0067] Preferably, the stability analysis unit 1105 is used to analyze transient stability according to the type of saturated element.

[0068] Preferably, the stability analysis unit 1105 performs transient stability analysis based on the type of saturated stage, including: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value. I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > id and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which, i dref , i d These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

[0069] The network-type VSC transient stability analysis system 1100 that takes into account the dynamic effects of the inner loop in an embodiment of the present invention corresponds to the network-type VSC transient stability analysis method 100 that takes into account the dynamic effects of the inner loop in another embodiment of the present invention, and will not be described again here.

[0070] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0071] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated otherwise.

[0072] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A transient stability analysis method for a network-type VSC considering the dynamic influence of the inner loop, characterized in that, The method includes: The control system of GFM-VSC is determined, and the active power and virtual power angle are determined based on the virtual synchronous power outer loop control. The phase of the port node voltage and the amplitude of the internal potential are determined based on the active power and the virtual power angle. The output current amplitude of the GFM-VSC is determined based on the internal potential amplitude and the virtual power angle. Based on the internal potential amplitude and the output current amplitude, determine whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, determine the type of saturation circuit. Transient stability analysis is performed based on the type of saturated process.

2. The method according to claim 1, characterized in that, Determining active power and virtual power angle based on virtual synchronous power outer loop control includes: ， Where P is the active power; δ This is a virtual work angle; P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

3. The method according to claim 1, characterized in that, Determining the port node voltage phase and internal potential amplitude based on the active power and virtual power angle includes: ， ， in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

4. The method according to claim 1, characterized in that, The output current amplitude of the GFM-VSC is determined based on the internal potential amplitude and the virtual power angle, including: ， Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

5. The method according to claim 1, characterized in that, Based on the internal potential amplitude and the output current amplitude, it is determined whether the GFM-VSC has triggered a saturation circuit, and when it is determined that a saturation circuit has been triggered, the type of saturation circuit is determined, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

6. The method according to claim 1, characterized in that, Transient stability analysis is performed based on the type of saturated process, including: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value. I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which, i dref , i d These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

7. A network-type VSC transient stability analysis system considering the dynamic effects of the inner loop, characterized in that, The system includes: The first calculation unit is used to determine the control system of GFM-VSC, and determines the active power and virtual power angle based on the virtual synchronous power outer loop control. The second calculation unit is used to determine the voltage phase and internal potential amplitude of the port node based on the active power and virtual power angle. The third calculation unit is used to determine the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle. The judgment unit is used to determine whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and to determine the type of saturation circuit when it is determined that a saturation circuit has been triggered. The stability analysis unit is used to analyze transient stability based on the type of saturated element.

8. The system according to claim 7, characterized in that, The first calculation unit determines the active power and virtual power angle based on the virtual synchronous power outer loop control, including: ， Where P is the active power; δ This is a virtual work angle; P N These are the rated active and reactive power settings; J This is the virtual inertia coefficient; K P This is the active frequency droop factor; D P This is the virtual damping coefficient; ω N These are the rated angular frequencies; δ and ω ref These are the virtual power angle and the virtual angular frequency, respectively.

9. The system according to claim 7, characterized in that, The second calculation unit determines the port node voltage phase and internal potential amplitude based on the active power and virtual power angle, including: ， ， in, θ The phase of the port node voltage; P is the active power; U g This refers to the voltage amplitude at the grid-side power supply node. U VSC This refers to the voltage amplitude at the port node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

10. The system according to claim 7, characterized in that, The third calculation unit determines the output current amplitude of the GFM-VSC based on the internal potential amplitude and the virtual power angle, including: ， Where I is the output current amplitude; U g This refers to the voltage amplitude at the grid-side power supply node. X L E is the reactance of the grid-connected line; E is the amplitude of the internal potential. δ This is a virtual work angle; X F To equip with filter reactors.

11. The system according to claim 7, characterized in that, The judgment unit determines whether the GFM-VSC has triggered a saturation circuit based on the internal potential amplitude and the output current amplitude, and determines the type of saturation circuit when it is determined that a saturation circuit has been triggered, including: If satisfied If so, the saturation process will not be triggered; If not satisfied Then the saturation stage is determined to be triggered, where if Then the trigger current saturation stage is determined; if Then, the internal potential limiting circuit is triggered; where I is the output current amplitude and E is the internal potential amplitude.

12. The system according to claim 7, characterized in that, The stability analysis unit performs transient stability analysis based on the type of saturated element, including: When the current saturation circuit is triggered, if the reference value and the actual value of the inner loop voltage under the current saturation state at the instant of disturbance clearance satisfy the following: Then the voltage inner loop control lowers the current reference value. I ref The GFM-VSC enters the desaturation process; if the reference value and actual value of the inner loop voltage under the current saturation state dominated by the disturbance clearance instant do not meet: If this fails, the negative feedback regulation mechanism of the voltage and current inner loop control will be ineffective, and the voltage inner loop control will be unable to lower the current reference value. I ref When the power outer loop recovers to an unexpected stable equilibrium point under current saturation, the GFM-VSC enters a saturation instability mode dominated by current limiting; among which, u d and u derf These are the instantaneous value of the d-axis port voltage and the reference value of the d-axis port voltage, respectively; the unintended equilibrium point under current saturation is the stable equilibrium point where the power reference value intersects with the power angle curve under current saturation. When the internal potential limiting circuit is triggered, if the reference value and actual value of the inner loop current under the dominance of the internal potential saturation state at the instant of disturbance clearance satisfy the following: Then the inner current loop integrator begins to desaturate. E Gradually decrease, and when E < E max At that time, GFM-VSC exits the saturation state; if the disturbance is cleared instantaneously, the condition is met. i dref > i d and i qref > i q If this occurs, the negative feedback regulation mechanism of the inner current loop control fails, and the internal potential... E When the power outer loop recovers to an unexpected stable equilibrium point under the internal potential saturation state, the GFM-VSC enters a saturation instability mode dominated by the internal potential; among which, i dref , i d These are the reference and actual d-axis current values ​​for the output current of the GFM-VSC, respectively. i qref , i q These are the q-axis current reference value and actual value of the output current of the GFM-VSC, respectively; the unintended equilibrium point under the internal potential saturation state is the stable equilibrium point where the power reference value and the power angle curve under the internal potential saturation state intersect.

Images