Control strategy without phase‐locked loop based on power estimation and natural frame for single‐phase cascaded H‐bridge converter

Abstract

Based on a single-phase cascaded H-bridge (CHB) multilevel converter, this paper investigates a control strategy combining power estimation and natural frame control (NFC) with the omission of grid voltage sensors. Besides, this control method, without phase-locked loop (PLL), can meet the continuous operation of the system and also eliminates grid voltage feedforward. First, natural frame control is introduced to derive the implementation process of control strategy without PLL, and the calculation formula of AC reference currents is given. Furthermore, the separate control of active and reactive currents is achieved. Second, the principle of proposed control algorithm is presented, and the sinusoidal voltage unit vector for synchronization can be accurately estimated. Next, considering the errors, the article corrects the method through parameter compensation. In addition, the balanced control method stabilized the DC side voltage of the converter. Finally, the effectiveness of this method is verified by computer simulation and experimental prototype.