Direct power control method of modular multilevel wind power converter

Abstract

The invention discloses a direct power control method of a modular multilevel wind power converter. The direct power control method includes: computing active power and reactive power through a virtual magnetic linkage, equaling a power grid to an ideal voltage source, combining the ideal voltage source with converter input reactance, equaling a grid-side power source to a virtual alternating-current motor, and considering that grid-side voltage is generated by the virtual magnetic linkage by sensing. Compared with a voltage-oriented double-closed-loop control method, the direct power control method does not need design of a current inner loop and is rapid in dynamic response; and compared with a look-up-table direct power control method, the direct power control method does not need a grid-side voltage sensor and is rapid in dynamic response, constant in switching frequency and better in steady-state characteristic.

Description

technical field [0001] The invention relates to the field of offshore wind power conversion technology, in particular to a direct power control method of a modular multilevel wind power converter. Background technique [0002] Large-scale grid-connection of renewable energy such as offshore wind energy has become the development direction of future power systems and smart grid applications. The application of voltage source converter-high voltage direct current transmission (VSC-HVDC) technology based on voltage source converter to long-distance transmission in offshore wind farms has become one of the current research hotspots. The VSC-HVDC system puts forward extremely high requirements on the capacity and voltage level of the voltage source converter. The modular multilevel converter (MMC) has the characteristics of a cascaded converter, which is easy to realize a large number of levels and a modular design, and can realize back-to-back connection on the DC side. It is a...

AI Technical Summary

Problems solved by technology

However, this method has the following deficiencies: 1. There are too many design parameters of the PI regulator, making it difficult to adjust

Most of the engineering setting methods are based on the system transfer function, but this type of system is relatively complex. Most of the PI parameters obtained by the equivalent calculation method of the simplified transfer function have large deviations, and need to be adjusted manually on site, and the system performance cannot be guaranteed.

2. There is a certain dependence on the system parameters. The inner loop feedforward structure needs to use parameters such as system inductance. In the actual system, the accuracy of these parameters is difficult to guarantee, sometimes the deviation is large, and with the change of the system operating conditions Different, there will be certain changes, therefore, often cause the actual operating performance of the PI regulator designed according to the nominal system parameters to deviate from the expected performance

3. The mathematical model of the light DC transmission system itself has strong coupling and nonlinear characteristics, and the PI regulator is designed according to the steady-state linearization model of the system. Therefore, the dynamic performance of the system cannot be guaranteed, and the adjustment effect cannot be optimal.

However, its obvious disadvantage is that the switching frequency of the converter is unstable, and the steady-state characteristics are not as good as VOC. At the same time, because more sensors are used, the system cost increases and the volume is large. Noise interference, causing system performance degradation

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