A novel soft-start method for SVG based on D-axis orientation

Abstract

In this paper, a novel method for shock-free soft-start is proposed. The novel method can realize the aim of no-overshoot and inrush of current during the entire soft-start process, thus the start process is safe, stable, and reliable. When the uncontrolled rectification stage ends, a sinusoidal signal synchronized with the grid voltage is generated through dq coordinate transformation and D-axis orientation, then the signal is transmitted to the three-phase inverter bridge. The AC voltage output of the inverter bridge is superimposed on both ends of the soft-start resistor along with the grid. The open-loop control method is adopted to gradually reduce the modulation ratio of the sinusoidal PWM wave until the capacitor voltage on the DC side reaches the rated voltage value, then the soft-start resistor is removed, which means the shock-free soft-start process is completed. Experimental results prove the effectiveness and feasibility of the control strategy proposed in this paper.

Adaptability Analysis of Differential Protection for Output Transformers in Wind Power Plants

“…If the rotor current exceeds the set value during a fault, the crowbar circuit is used to shortcircuit the rotor winding and converter. [4][5] Consuming power on the current limiting resistor to reduce the fault current on the rotor side by selecting a suitable current limiting resistor with a suitable resistance value, the voltage borne by the converter switch tube is kept within a safe range. At the same time, the pitch angle is adjusted to reduce the fan speed to prevent overspeed shutdown, so that all parts of the doubly fed fan are not damaged during the fault period and maintain grid connection operation until the fault is removed or the time required for low-voltage crossing is reached before grid disconnection.…”

Frequency, Phase, and Magnitude Difference Locked-Loop Based Linear Synchronization Scheme for Islanded Inverters and Microgrids

“…Different methods for commissioning microgrid inverters have been proposed in the literature, such as soft-start, soft-commissioning, and black start [43], [44], [96], [97], [98], [99]. However, special control methods are needed after synchronization to commission the inverters in islanded microgrids.…”