Symmetrical fault ride-through control method of double-fed wind generator set

Abstract

The invention discloses a symmetrical fault ride-through control method of a double-fed wind generator set. Under a grid fault of the double-fed wind generator set, a rotor Crowbar circuit of the double-fed wind generator set starts operation, and a rotor converter is locked at the same time when the current flowing to the rotor converter exceeds the maximum allowable current of the rotor converter. During the occurrence of the fault, the rotor Crowbar circuit is cut off, and the rotor converter is restarted at the same time when the rotor current value is smaller than a Crowbar protection action threshold value after the rotor Crowbar circuit enters tauonr duration. After the fault is removed, the rotor converter is switched to be in an active power work mode by recovering the control strategy, and stops injecting the passive current to a grid. The method provided by the invention can overcome the disadvantages in the existing fault ride-through control strategy, thereby improving the fault ride-through capacity of the double-fed wind generator set.

Description

technical field [0001] The invention relates to the technical field of new energy power supply control, in particular to a symmetrical fault ride-through control method for a doubly-fed wind power generating set. Background technique [0002] At present, for the most widely used doubly-fed wind turbines in wind farms, a sudden drop in the stator voltage of the generator during a fault will cause a large attenuated DC component in the stator flux linkage. Due to the electromagnetic coupling relationship between the stator and rotor windings of the generator, the DC component of the stator flux linkage will induce large transient voltage and current in the rotor winding. However, the rated capacity of the converter connected to the rotor winding of the doubly-fed wind turbine is relatively small (only 20%-30% of the rated capacity of the unit), and the converter itself has poor overcurrent and withstand voltage capabilities, so the power grid failure It poses a great threat t...

AI Technical Summary

Problems solved by technology

[0003] However, the existing fault ride-through control technology based on the rotor crowbar circuit only considers the switching control of the rotor crowbar circuit from the perspective of protecting the converter. This is because when the crowbar circuit is put into operation (rotor winding side conversion DFIG is in an uncontrollable state of asynchronous power generation, especially when the Crowbar circuit is put into operation for a long time, the generator will absorb a large amount of reactive power from the grid, which is not only very unfavorable to the voltage stability of the connected grid It cannot effectively guarantee the rapid recovery of the wind turbine to normal operation after the fault is removed.

In addition, most of the existing LVRT control strategies also take the DC bus voltage as one of the switching conditions of the rotor crowbar circuit, ignoring the root cause of the DC bus voltage change during the fault period.

In fact, the DC bus voltage is related to the power flow direction and size of the grid-side and rotor-side converters connected on both sides, and the switching control of the rotor crowbar circuit alone cannot ensure that the DC voltage can be maintained in the DC bus capacitor during a fault. or the voltage tolerance range of the converter, once the voltage exceeds the above range, the generator set will be forced to be cut off from the grid due to the protective action of the capacitor or the converter itself

[0004] At the same time, the existing low-voltage ride-through control strategies rarely involve how to quickly restore the normal operation of the DFIG after the fault is removed. The large attenuation DC component in the stator flux linkage of the generator caused by the sudden change of the machine terminal voltage will also directly affect the rotor voltage and current

However, the adjustment and control capabilities of the converter itself are limited, and the wind turbine will not be able to reach a stable operating state if no appropriate control strategy is adopted after the fault is removed.

It can be seen that the existing fault ride-through control strategy of double-fed wind turbines cannot well meet the low-voltage ride-through capability of wind turbines required by the new grid regulations.

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