Power Calculation for Direct Power Control of Single-Phase Three-Level Rectifiers Without Phase-Locked Loop

Synchronization unit such as single-phase grid voltage phase-locked loop (PLL) is essential to control scheme in single-phase converters. However, the design of PLL is not simple and increases the complexity of control system, and the performance of PLL could be impacted by the waveform quality of the main voltage. Therefore, in this paper, a novel single-phase power calculation method without PLL is proposed to improve the performance of single-phase three-level rectifier which is widely used in railway traction drive system. Moreover, a strategy to compensate phase angle and power calculation error is presented to improve the power calculation precision and enlarge operation range. Then the compensation strategy and the single-phase power calculation method are combined with a common direct power control (DPC) to form a no-PLL control system for single-phase three-level rectifiers. Finally, performance of the proposed scheme is verified through experimental tests and compared with two traditional PLL-based control schemes.