Improved Capacitor Voltage Feedforward for Three-Phase LCL-Type Grid-Connected Converter to Suppress Start-Up Inrush Current

Abstract

Three-phase active damping LCL-type grid-connected converters are usually used in distributed power generation systems. However, serious inrush current will be aroused when the grid-connected converter starts, especially in rectifier mode, if no effective control method is taken. The point of common coupling (PCC) voltage feedforward is usually used to suppress start-up inrush current. Unfortunately, it will introduce a positive feedback loop related to the grid current and grid impedance under weak grid conditions, and therefore, the grid current will be distorted and the system stability margin will be significantly reduced. To solve the above problems, this paper proposes a simple method based on a d-axis fundamental positive-sequence component of filter capacitor voltage feedforward, without extra sensors and software resources. With the proposed method, it is possible to suppress the start-up inrush current and maintain the grid current quality and system stability under weak grid conditions. The mechanism of start-up inrush current and the effectiveness of the method for inrush current suppression are analyzed in detail. Then, the influences of different feedforward methods on system stability are analyzed under weak grid conditions by the impedance model of grid-connected converter. Finally, experimental results verify the validity of the proposed method.

Dissipativity Robustness Enhancement for LCL-Filtered Grid-Connected VSCs With Multisampled Grid-Side Current Control

“…According to (18), the non-dissipative region considering filter parameter variation is obtained as ( , ) or ( , ).…”

“…The expression of Yo,con(s) and its real part are given in (31) and (32). Considering L1=kL1norm and C=kCnorm, the nondissipative region with the CCAD is the same as (18). As depicted in Fig.…”

“…However, the antiresonance frequency of the LCL filter shall be constrained to a specific range, which limits the design of the converter-side inductor and the filter capacitor [13,15,16]. In addition, the grid voltage feedforward is often ignored when designing the high-frequency dissipativity, hence the transients during the start-up or grid disturbances cannot be addressed [18][19].…”

Wideband Dissipativity Enhancement for Grid-Following VSC Utilizing Capacitor Voltage Feedforward

“…Besides, the above-mentioned methods neglect the impact of the proportional CVF, which is often required during the startup or grid disturbances [28]. Although the high-frequency dissipative region can be extended with the CVF, lowfrequency dissipativity deteriorates due to the interaction of the CVF and alternating-current control (ACC) and PLL [11,26].…”

Modeling and Enhanced Error-Free Current Control Strategy for Inverter with Virtual Resistor Damping

“…The harmonic component control with virtual resistor damping is not analyzed [25][26][27][28]. Second, for inverter-side current control, capacitor voltage contributes to stabilize the system [29][30][31].…”