A method for overvoltage suppression control of flexible direct current transmission wind power grid-connected converter

Abstract

The invention discloses an overvoltage suppression control method of a flexible direct-current transmission wind power grid-connected converter. The method comprises the steps: subtracting an averagevalue of a sum of three-phase capacitor voltages from the capacitor voltage of each phase, and obtaining a compensation component of each phase after proportional integral control; comparing the average value of the sum of three-phase module voltages after low-pass filtering with a set value, and when a comparison result outputs enabling, sending a difference value between the average value of thesum of the three-phase module voltages and the set value to PI control to obtain a direct-current common-mode compensation component of a three-phase modulation voltage; and adding the compensation component of each phase to a direct-current common-mode compensation component to serve as a total overvoltage compensation component. In the invention, two overvoltage components are suppressed, a problem that overvoltage protection is performed before an energy consumption device is started due to a fact that a certain phase voltage is too high under a condition of a three-phase asymmetric faultis solved, a voltage of a direct current bus can be actively increased when the average voltage of the module reaches a critical stable set value, a direct current is limited, the energy consumption device is promoted to be started, and passive overvoltage protection is avoided.

Description

technical field [0001] The invention relates to the technical field of flexible direct current transmission systems, in particular to an overvoltage suppression control method for wind power grid-connected converters of flexible direct current transmission. Background technique [0002] The voltage source converter based on MMC topology has the advantages of independent adjustment of active power and reactive power at the same time, no commutation failure problem, power supply to passive systems, and low harmonic level. It is mainly used in wind power grid-connected and isolated islands. Power supply, asynchronous networking and other fields of direct current transmission, energy storage, and reactive power compensation are research hotspots and development directions in the field of power electronic converters, especially in the field of offshore wind power grid integration, with great prospects. [0003] With the development of flexible DC projects to high voltage and high...

AI Technical Summary

Problems solved by technology

Since the power of the offshore wind farm cannot be reduced instantaneously, the onshore station converter will be equipped with an energy release device, but the energy release device is installed between the poles to control the voltage between the poles on the DC side. If there is a symmetrical fault, the capacitor voltage between the bridge arms will be unbalanced, and the unbalanced voltage can be as high as several hundred volts per module on average. When the pole line voltage exceeds the start-up threshold of the energy release device, some bridge arms may have been severely overvoltage and tripped. up

In addition, in order to avoid the fluctuation and interference of the DC bus due to measurement or transient current, the voltage start-up threshold of the energy release device is set too high, generally around 1.3p.u. of the rated voltage or even higher. Excessive DC voltage may cause commutation The valve runs near the critical safety operating point, which is not conducive to the safety of the converter valve

Images