Parallel-in converter for directly-driving wind power generation system

Abstract

Disclosed are a grid-connected converter device of a direct-drive wind power system and a corresponding power coordination control method. The converter device is composed of basic converter units of a Boost circuit based on ac-side energy storage; the structure sufficiently utilizes the equivalent inductance of a power generator stator winding, avoids an external inductor in traditional dc voltage booster circuit, and reduces power loss and equipment cost. Two converter proposals, including a diode rectification mode and a PWM rectification mode are designed; converter topologies with two capacity grades, including medium and small power converter topology, megawatt grade high power converter topology, and relative extension structures are designed, such as a parallel connection converter and an H bridge cascade structure converter; wherein, the converter with the H bridge cascade structure is applicable to grids with high capacity and high voltage, and can obviously reduce the harmonic content in grid-connected current; meanwhile, the control method performing feedback through three closed loops is designed, so the input power and output power of the converter are balanced instantaneously, the dc bus voltage maintains stable, and the grid-connected current wave is sine.

Description

technical field [0001] The invention relates to the field of energy technology, in particular to the grid-connected converter technology of a direct-drive wind power generating set. Background technique [0002] With the continuous development of renewable energy, the power generation of wind turbines is increasing, and the requirements for reliability and efficiency of wind turbines are also increasing. The existence of gearboxes limits the development of double-fed wind turbines. It is in this case that the direct drive wind power generation system appears. The synchronous generator used in the direct-drive wind power generation system adopts a special design scheme, and its large number of pole pairs enables the generator to still work efficiently when the rotor speed is low; in the direct-drive wind power generation system, the wind turbine Directly coupled with the rotor of the synchronous generator, eliminating the need for a gearbox, improving efficiency, reducing ge...

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Problems solved by technology

[0003] Among the various converter schemes of the direct-drive wind power generation system, the structure control of the back-to-back converter widely studied at present is relatively complicated, and the cost is high, which hinders the promotion speed of the direct-drive wind power generation set; and the simple The converter structure composed of an uncontrolled rectifier circuit and a PWM inverter circuit has certain practicability, but this structure cannot effectively control the wind generator, which limits its available wind speed range, and the wind turbine required Multiple control objectives such as maximum power tracking control and grid-connected current control are difficult to balance; in this case, a new scheme of introducing a DC-DC structure Boost circuit into the DC link of the converter It can overcome the above shortcomings, but it also introduces certain problems: the traditional DC-DC Boost circuit needs a large energy storage inductance, and it needs to be equipped with a bulky and cumbersome inductance device; at the same time, under high-power application conditions , the current flowing in the energy storage inductor is a unidirectional triangular wave current. The current not only has a DC component, but also contains a large high-frequency switching component. The inductor needs an iron core of high-frequency material. In addition, because the inductor current is unidirectional, the iron The residual magnetism of the core will gradually increase due to the cumulative effect, causing the inductance to be easily saturated, which brings great difficulties to the manufacture of the energy storage inductance and increases the manufacturing cost; at the same time, the energy storage inductance is not only heavy and bulky, but also brings Severe heat generation problem. At present, most of the inductors use imported products, which are expensive

Chinese patent CN2909689Y discloses a "high-efficiency three-phase power factor correction bipolar output circuit", and Chinese patent CN101060252A discloses an "uninterruptible power supply device". The circuit structures in the above inventions are all used for voltage and frequency All stable three-phase power grids require a separate configuration of three-phase AC inductance devices, and are not suitable for special applications of wind power generation, that is, high-power applications where the amplitude and frequency of the power supply on the input side change randomly

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