Power fluctuation and fault control system and method for DC transmission doubly-fed wind turbines

Abstract

The invention relates to a power fluctuation and malfunction control system and method of a direct-current-transmission double-fed wind turbine set, and belongs to the field of wind power. The system includes a double-fed power generator, a stator-side converter, a rotor-side converter, a net-side direct-current converter and an energy storage system. According to the method, firstly, the energy storage system supplies power to the rotator-side converter to achieve inverse conversion; secondly, after a draught fan is enabled, the stator-side converter conducts rectification boosting, the net-side direct-current converter conducts constant power control and controls the energy storage system to charge and discharge electricity to achieve power fluctuation suppression; if voltage drop occurs to a power network, the net-side direct-current converter conducts constant direct voltage control, and the rotator-side converter and the energy storage system run in a voltage drop malfunction control mode; if overvoltage occurs to the power network, the energy storage system conducts voltage clamp on the power network; if the network is disconnected, the net-side direct-current converter conducts constant direct voltage control, the rotator-side converter makes the output power of the power generator turn to zero; and finally, the net-side direct-current converter is switched off. The power fluctuation and malfunction control system and method of the direct-current-transmission double-fed wind turbine set are conducive to usage of the double-fed wind turbine set in a flexible direct current transmission system.

Description

technical field [0001] The invention relates to a control system and a control method, in particular to a power fluctuation and fault control system and method of a DC transmission doubly-fed wind turbine, belonging to the technical field of wind power generation. Background technique [0002] Doubly-fed wind turbines are one of the most widely used mainstream products in the wind power market. Traditional doubly-fed wind turbines use small-capacity back-to-back converters connected to the generator rotor, while the generator stator is directly connected to the grid. Therefore, when the grid voltage drops and fails, the flux linkage of the generator stator will be broken. Oscillation, so that the stator flux linkage contains DC components, and there will be negative sequence components for asymmetric grid voltage drops. The doubly-fed generator has a higher speed, so the DC component and negative sequence component in the stator flux linkage will have a higher slip rate, wh...

AI Technical Summary

Problems solved by technology

Traditional doubly-fed wind turbines use small-capacity back-to-back converters connected to the generator rotor, while the generator stator is directly connected to the grid. Therefore, when the grid voltage drops and fails, the flux linkage of the generator stator will be broken. Oscillation, so that the stator flux linkage contains DC components, and there will be negative sequence components for asymmetric grid voltage drops

The doubly-fed generator has a higher speed, so the DC component and negative sequence component in the stator flux will have a higher slip rate, which will cause overcurrent or overvoltage in the rotor circuit of the generator.

[0003] At present, the low-voltage ride-through of the traditional doubly-fed wind turbine usually adopts the crowbar protection circuit (crowbar circuit). The principle is to use the resistance to consume the excess energy on the rotor side. The disadvantage is that once the crowbar circuit is put into operation, the rotor winding of the generator will be short-circuited, so that the doubly-fed generator becomes a squirrel-cage asynchronous generator, and a large amount of reactive power needs to be absorbed from the grid for excitation, which will be detrimental to the grid The grid voltage recovers quickly after the fault, and the resistance not only wastes energy, but also raises the temperature inside the cabinet, threatening the safety of the power devices of the converter

In addition, the input and cut-off time of the crowbar circuit is very important. Improper selection will cause multiple actions of the crowbar circuit on the one hand, and may cause a large current shock on the other hand.

[0004] It can be seen that the traditional doubly-fed wind turbine has inherent defects: 1) The low voltage ride-through capability of the system is poor: once the grid voltage drops, the stator voltage of the generator will drop, especially when the grid voltage drops sharply, the stator and rotor will A large fault current is caused in the winding, and the DC bus voltage will also rise rapidly, seriously endangering the safety of the wind turbine

2) Poor control of the crowbar protection circuit will cause greater harm and is not conducive to the restoration of the grid voltage, and the resistance will waste energy and increase the heat dissipation pressure of the converter cabinet

[0005] In recent years, flexible DC transmission technology has attracted much attention due to its advantages of reliable operation, simple control, and low cost. Also began to discuss the application of flexible DC transmission technology in doubly-fed wind farms, where DC transmission lines may have voltage dips (usually caused by single-phase grounding), overvoltage, DC transmission line disconnection and other faults, which seriously threaten the system. Safe operation, there is little research in this area

[0006] In addition, changes in wind speed will cause fluctuations in the output power of wind turbines, which will affect the stability of the output power of wind turbines.

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