CN-116865252-B - Transient stability control and analysis method based on network-structured VSC current limiting strategy

CN116865252BCN 116865252 BCN116865252 BCN 116865252BCN-116865252-B

Abstract

The invention discloses a transient stability control and analysis method based on a grid-structured VSC current limiting strategy, which comprises the steps of 1, adopting an anti-integrator saturation module in a voltage control loop, 2, introducing a current saturation angle and determining the optimal value of the current saturation angle, 3, improving the VSC current limiting module based on the introduced current saturation angle, and 4, analyzing the transient stability of a system by utilizing a phase diagram based on the current limiting module and the current saturation angle. According to the invention, the transient stability control is carried out by introducing a current saturation angle, so that the transient stability of a system formed by the grid-structured VSC and an infinite power grid can be effectively improved, and the transient stability of the grid-structured VSC is qualitatively analyzed through a phase diagram.

Inventors

MENG XIAOXIAO
WANG YUCHEN
MAO XUN

Assignees

合肥工业大学
国网安徽省电力有限公司电力科学研究院

Dates

Publication Date: 20260512
Application Date: 20230707

Claims (4)

1. The transient stability control method based on the network-structured VSC current limiting strategy is characterized by comprising the following steps of: step S1, designing an anti-saturation module of an integrator in a voltage control loop, so as to shield the integrator under the current limiting strategy by using a formula (1): (1) In the formula (1), I dref and I qref are respectively d-axis and q-axis current reference values output by a voltage control loop, I s is dq-axis synthesized current, I m is the maximum value of saturation current, y is the output of an anti-integrator saturation module, an integrator of the voltage control loop is not shielded when the output is 1, and an integrator of the voltage control loop is shielded when the output is 0; s2, introducing a current saturation angle and determining the optimal value of the current saturation angle: Defining d-axis and grid voltage in dq coordinate system of voltage source converter VSC Angle between (2) As the virtual power angle, when the power grid is operating normally, calculating the active power P and the reactive power Q output by the VSC in steady state by the formula (2): (2) In the formula (3), R and X are equivalent resistance and equivalent reactance between the VSC and an infinite power grid respectively, and U and E are the voltage amplitude of a public coupling point and the voltage amplitude of the power grid respectively; Defining the current saturation angle phi as the included angle between the maximum value I m of the saturation current and the d axis, and calculating the active power output by the VSC by the formula (3) after the fault: (3) in the formula (3), the amino acid sequence of the compound, Active power output by the VSC after the fault; The amplitude of the voltage drop of the power grid after the fault; using the constraint of the current saturation angle phi of formula (4): (4) taking into account the variation of the short-circuit ratio SCR, the optimum value phi opt of the current saturation angle phi is obtained by using the formula (5): (5) In formula (5), SCR min and SCR max are the maximum and minimum values of the short circuit ratio SCR, respectively; s3, designing a current limiting module by using a formula (6), and controlling a saturated current angle phi so as to control transient stability of a system formed by the grid-structured VSC and an infinite power grid: (6) In formula (6), I drefs and I qrefs are d-axis and q-axis current references output by the current limiting module, respectively.
2. A transient stability analysis method based on a network-structured VSC current limiting strategy is characterized in that the transient stability analysis method is based on the transient stability control method of claim 1, the transient stability of a system formed by the network-structured VSC and the infinite power grid is analyzed by using a phase diagram, and the method comprises the following steps: S4, based on the current limiting module and the current saturation angle phi: S4.1, obtaining a control formula of the active loop and the reactive loop of the VSC by using a formula (7): (7) In the formula (7), omega vsc and omega 0 are output frequency and frequency reference values of the VSC respectively, J is rotational inertia, D p is a damping coefficient, P ref is a reference value of active power of the VSC, Q ref is a reference value of reactive power of the VSC, K q is a reactive integration coefficient, U 0 is a voltage reference value of the VSC, and s is a Laplacian operator; S4.2. formula (8) is obtained from formula (7): (8) S4.3. let variable x 1 = Variable x 2 = The variable x 3 =u, thereby constructing the state equation before the fault occurs using equation (9): (9) In the formula (9), the amino acid sequence of the compound, 、 And The derivatives of x 1 、x 2 and x 3 with respect to time are shown, respectively; S4.4, constructing a state equation after the fault occurrence by using the formula (10): (10) And S4.5, drawing a phase diagram according to the two state equations so as to obtain a transient stability analysis result of the system.
3. An electronic device comprising a memory and a processor, wherein the memory is configured to store a program that supports the processor to perform the transient stability control and analysis method of claim 1 or 2, the processor being configured to execute the program stored in the memory.
4. A computer readable storage medium having stored thereon a computer program, characterized in that the computer program when run by a processor performs the steps of the transient stability control and analysis method of claim 1 or 2.

Description

Transient stability control and analysis method based on network-structured VSC current limiting strategy Technical Field The invention relates to the field of transient stability control and analysis of a network-structured VSC, in particular to a transient stability control and analysis method based on a network-structured VSC current limiting strategy. Background New energy power generation will be greatly developed in the future. The new energy power generation system is connected into a power grid through a voltage source converter (voltage source converter, VSC), and a large number of new energy power generation systems exist in the power grid in the future. The VSC has the advantages of complete controllability, and can realize power conversion and transmission by different control means according to different characteristics of renewable energy sources and the intensity of a power grid. Droop control mimics the dynamics of a conventional synchronous machine (synchronous generator, SG) in terms of frequency and voltage regulation, but lacks inertia. VSCs controlled with virtual synchronous machines (virtual synchronous generator, VSG) have damping characteristics and inertial characteristics similar to conventional synchronous machines, with the ability to respond to regulation requirements of the grid. Special care is required for over-current protection due to the voltage source characteristics of the grid-type VSC. The grid-built VSC can only cope with typically 20% of the over-current, compared to synchronous generators which can support up to seven times their rated current. Therefore, the grid-connected converter must rely solely on control to prevent extreme faults such as short circuits, heavy-load connections, line jumps/recloses, and voltage phase jumps, while maintaining synchronization with the power system. In order to limit the current during large transients, many control strategies have been proposed for a grid-type VSC. One strategy is to limit the current using a Current Saturation Algorithm (CSA). In practice, this technique is implemented on the VSC generated reference current by saturating the reference current during the over-current. Another well-known current limiting strategy is based on a Virtual Impedance (VI) which mimics the effect of the impedance when the current exceeds its nominal value. The method has been shown to limit the effectiveness of current transients in various event situations while maintaining the voltage source characteristics of the power converter. However, the current limiting strategy also has the problems of difficult mode switching, complex parameter design, difficult recovery after failure and the like. Therefore, how to improve the current limiting strategy, evaluate the transient stability of the VSC by a new method, and realize the analysis and control of the transient stability is a problem that needs to be solved by those skilled in the art. Disclosure of Invention Aiming at the problem that the current limiting strategy of the existing network-structured VSC is applied to the transient stability analysis control, the invention provides a transient stability control and analysis method based on the current limiting strategy of the network-structured VSC, so that the transient stability of a system formed by the network-structured VSC and an infinite power grid can be effectively improved, and the transient stability of the network-structured VSC is qualitatively analyzed through a phase diagram. In order to achieve the aim of the invention, the invention adopts the following technical scheme: The invention discloses a transient stability control method based on a network-structured VSC current limiting strategy, which is characterized by comprising the following steps: step S1, designing an anti-saturation module of an integrator in a voltage control loop, so as to shield the integrator under the current limiting strategy by using a formula (1): In the formula (1), I dref and I qref are respectively d-axis and q-axis current reference values output by a voltage control loop, I s is dq-axis synthesized current, I m is the maximum value of saturation current, y is the output of an anti-integrator saturation module, an integrator of the voltage control loop is not shielded when the output is 1, and an integrator of the voltage control loop is shielded when the output is 0; s2, introducing a current saturation angle and determining the optimal value of the current saturation angle: Defining d-axis and grid voltage in dq coordinate system of voltage source converter VSC The angle delta' between the two is a virtual power angle, and when the power grid normally operates, the active power P and the reactive power Q output by the VSC in a steady state are calculated by the formula (2): In the formula (3), R and X are equivalent resistance and equivalent reactance between the VSC and an infinite power grid respectively, and U and E are the voltage amp