Operational curved surface method for determining asymmetric short-circuit current of distributed generation access power grid

Abstract

The invention discloses an operational curved surface method for determining asymmetric short-circuit current of a distributed generation access power grid. The method comprises steps of acquiring a three-node simplified network and transfer impedance between different nodes by using network simplification when multiple DGs and conventional generators have access to the power grid; in view of different types of asymmetric short-circuit faults, ignoring the influence of DG zero-sequence current injection, obtaining a short-circuit calculation compound sequence network and positive and negative sequence augmented networks according to a fault point boundary condition, and calculating the additional voltage and additional impedance in the augmented networks; performing Thevenin equivalent on systems except the DG access points in the positive and negative sequence networks, and deriving short-circuit impedance and open-circuit voltage open-circuit voltage computational formulas when DC injection current is zero; establishing a operational curved surface of a DG short-circuit current negative-sequence component, computing impedance, and positive and negative sequence open-circuit voltage in order to obtain a DG short-circuit current negative-sequence component; calculating a DG asymmetric short-circuit current positive-sequence component in combination with a three-phase short-circuit operational curved surface according to a DG access positive-sequence augmented network access point equivalent open-circuit voltage computing method.

Description

technical field [0001] The invention relates to the technical field of distributed power generation systems, in particular to a calculation surface method for determining the asymmetric short-circuit current of distributed power generation connected to a power grid. Background technique [0002] With the intensification of environmental pollution and the increasing shortage of energy, countries have begun to develop wind energy, solar energy and other renewable energy on a large scale, and the corresponding distributed generation (DG) has been highly valued and vigorously developed. However, the access of DG changes the power flow and short-circuit current distribution of the power grid, and the fault current provided by DG will affect the original protection of the line and the coordination action of reclosing devices. In order to ensure the safe and stable operation of DG connected to the power grid, the "Technical Regulations for Distributed Power Generation Connected to ...

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Problems solved by technology

[0003] With the gradual opening of wind power and photovoltaic grid-connected services, their operation scale continues to expand. However, a large number of DG connections have brought many adverse effects on the safe and stable operation of the power grid.

First of all, the connection of DG to the power grid will lead to major changes in the system structure, changing the power flow and short-circuit current distribution of the power grid, and the short-circuit current provided by it in the event of a fault will appear polymorphic due to the diversity of its parameters and operation and control methods

Secondly, the short-circuit current injected by a large number of DGs will increase the fault point current, which will lead to higher dynamic and thermal stability requirements for electrical equipment, and even exceed the breaking capacity of switchgear, forcing large-scale equipment upgrades

In addition, due to the uncertainty of DG output and the diversity of operation combinations, the variation range of short-circuit current will increase, and the coordination of protection and reclosing will become more difficult.

These will not only interfere with the power quality of the power grid, but also affect the accurate action of the relay protection device and affect the safe and stable operation of the power grid.

[0004] At present, there have been a large number of literatures on the short-circuit calculation model and algorithm of the power grid containing DG, mainly using the DG short-circuit calculation model and network equations to iterate interactively. The amount of calculation is large, which cannot meet the requirements of engineering calculation

The existing engineering practical algorithm is the calculation curve method in China and the calculation coefficient method in foreign countries, mainly for synchronous generators and induction motors, and has not yet given a practical short-circuit calculation method for wind power and photovoltaic generator sets

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