Tianjin University

Abb Research Ltd.

Yongli Li

Botong Li

Xiaolong Chen

Bin Li

Xiaowen Han

Bin Su

Li Chen

Yunke Zhang

Zhiying Yang

Jinzhao Song

A source-network coordination type direct-current (DC) circuit breaker based on pre-charged capacitors for an MMC based DC grid is provided. The MMC based DC grid is provided with four converter stations, each having two converters, which are in loop connection through a double-loop DC overhead line. Two ends of each DC line connecting the converters are separately equipped with DC circuit breakers for isolating a fault of the DC line. An MMC active voltage adjusting control strategy is matched with pre-charged capacitor voltage in the self-adaptive mode to provide a beneficial breaking condition for a quick mechanical switch branch, so that the fault line is effectively cut off.

Source-network coordination type direct-current (DC) circuit breaker based on pre-charged capacitors for modular multilevel converters (MMC) based DC grid

The invention discloses an islanding detection method in DC microgrids based on MPPT trapezoidal voltage disturbance. The steps are as follows: start the MPPT strategy; set the starting signal threshold of disturbance; measure the output current of PVA at the maximum power; calculate the same environmental factor of PVA with different capacities under the same light intensity and temperature in real time; when the environmental factor is greater than the starting signal threshold of the disturbance, periodic trapezoidal disturbance is carried out to the PVA port voltage reference; if the PCC voltage Upcc exceeds the threshold set by the passive method, it is judged as islanding; otherwise, it is judged whether the change rule of Upcc is consistent with the change rule of the calculated PCC voltage Upccp under the trapezoidal disturbance; If it is consistent, it is judged as islanding; otherwise, it is pseudo islanding.

Islanding detection method in DC microgrids based on MPPT trapezoidal voltage disturbance

The invention discloses an adaptive fault clearing scheme for an MMC VSC-HVDC grid based on source-grid coordination. A grid-side circuit breaker topology is disposed at each end of each DC line of the MMC VSC-HVDC grid to coordinate with a source-side control strategy when a fault occurs to the DC line so as to isolate the fault together. When a system runs stably, the voltage regulation controller does not actuate, after the fault occurs, the voltage regulation controller is started, and the output voltage regulation coefficient decreases, so that voltage at outlets of the converters drops accordingly, and coordinates with voltage of the pre-charging capacitor of the grid-side circuit breaker topology to realize fault isolation based on source-grid coordination. The adaptive fault clearing scheme provided by the invention greatly improves the speed of fault isolation.

Adaptive fault clearing scheme for MMC VSC-HVDC grid based on source-grid coordination

The invention relates to a grounding fault protection method for a high-voltage capacitor of a direct-current filter. The method comprises the following steps of acquiring a head end voltage u and an unbalanced current iof a direct-current filter, and acquiring a discrete head end voltage and unbalanced current sequence; calculating a virtual capacitance C; determining a protection setting value Caccording to the bridge arm capacitance of the high-voltage capacitor, and when the virtual capacitance Cis larger than the protection setting value C, protecting and judging to be an internal fault; otherwise, protecting and judging to be an external fault.

Grounding fault protection method for high-voltage capacitor of direct-current filter

A method for identifying the type of faults occurred on a power line, characterized in that it comprises: calculating a fault point voltage on fault points based on terminal voltage and fault locations of the power line; adopting the fault point voltage corresponding to a maximum transition resistance as a setting value; comparing the fault point voltage on fault points with the setting value; and identifying the type of fault as a permanent type or a transient type based on the result of the comparison.

Growing community of inventors

Tianjin, China

Yongli Li