Mixed convertor device and method suitable for double-fed wind turbine system

Abstract

The invention discloses a mixed convertor device and method suitable for a double-fed wind turbine system. The mixed convertor device comprises a double-fed wind turbine generator, a main transformer, a VSC and a CSC, wherein the VSC is connected between the generator rotor side and the low voltage side of the main transformer, the CSC is connected between the generator rotor side and the low voltage side of the main transformer, mixed conversion is carried out through the CSC and the VSC, the CSC of the mixed convertor device serves as a main convertor to bear most of circulation currents, and the VSC of the mixed convertor device serves as an auxiliary convertor to bear a small part of the circulation currents. The mixed convertor device has the advantages of a voltage source type converter and a current source type converter, the switch losses are reduced, the low-order harmonic content is reduced, meanwhile, the system response time is shortened, and oscillations of the current on the alternating current side are restrained.

Description

technical field [0001] The invention relates to the technical field of wind power generation, in particular to a converter device and method suitable for double-fed wind power generating sets. Background technique [0002] For doubly-fed wind turbines, due to the bi-directional flow of rotor energy, the rotor-side converter needs to be a bi-directional converter. At present, the converter topology that can be used in doubly-fed wind power generation systems is mainly AC-DC-AC Converter (AC-DC-AC Converter), which can be divided into voltage source AC-DC-AC Converter according to the difference of the intermediate DC energy storage link. (Voltage Source Converter, referred to as VSC) and current source AC-DC converter (Current Source Converter, referred to as CSC). [0003] The characteristic of VSC is that the energy storage element of the intermediate DC link adopts a large capacitor, and the reactive power of the system will be buffered by it. The DC voltage is relatively...

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Problems solved by technology

In the event of a fault, especially in the process of grid voltage drop or recovery, the DC inductance of CSC can limit the rate of change of current flowing through the power device and keep the DC current stable, thereby protecting the power device; but CSC also has shortcomings. Where, when the square wave modulation is used, the output of the converter contains relatively rich low-order harmonics, and due to the role of the double-fed motor rotor leakage inductance can generate a peak voltage that threatens the safety of the motor insulation, so in most of this type The converter is equipped with a parallel capacitor at its output to absorb the peak voltage. When PWM modulation is used, a parallel capacitor is also required at its output to absorb the ripple current.

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