Abstract
Power electronic transformer (PET) with modular cascaded structure has become a flexible interface between AC and DC grids. Nonetheless, the notable 2nd-order ripple power introduced from the AC source requires considerable energy storage in the module capacitors, which is likely to degrade the overall power density and increase system cost. In this paper, a power channel based four-winding PET (PC-PET) is proposed to address such an issue. Owing to the phase-crossing power channels, the low-frequency ripples can cancel each other through magnetic flux counteracting. To improve the accuracy of power decoupling, the effect compromised by inconsistent windings is considered. Accordingly, a proportional-resonant (PR) control based power decoupling strategy for PC-PET incorporated with power balance is proposed to decouple the three-phase low-frequency ripple powers, and minimize the voltage ripple in module capacitors. Additionally, the improvement of power density is discussed based on analyses on power losses, capacitor volume and transformer volume. Simulation and experimental results verified the validity of proposed control strategies.
Highlights
Power electronic transformer (PET) contributes to intelligent power flow management while providing reduced weight/volume, improved power quality, enhanced reliability and so forth [1]–[3]
Cascaded H-bridge (CHB) and modular multilevel converter (MMC) based PET are both with AC/DC-DC/HFAC-HFAC/DC configuration
The results reveal that the proposed power channel based PET (PC-PET) control strategy can effectively suppress the voltage ripple in module capacitors
Summary
Power electronic transformer (PET) contributes to intelligent power flow management while providing reduced weight/volume, improved power quality, enhanced reliability and so forth [1]–[3]. X. Li et al.: Capacitor Voltage Ripple Minimization of a Modular Three-Phase AC/DC PET powers are introduced from each AC-input-port and stored in DC capacitors of the modules. In order to reduce the 2nd-order ripple in capacitor voltage, large DC capacitance is usually required This will increase the volume of the system and reduce the power density. Power decoupling in single-phase PWM rectifier normally requires large passive capacitors to trap low frequency ripple powers [13]–[17]. The 2nd-order ripple voltage in module capacitors and operating principle of PC-PET are discussed. SECOND-ORDER RIPPLE VOLTAGE ANAYSIS AND OPERATING PRINCIPLE OF PC-PET The circuit of PC-PET is shown, with N modules in each phase leg (a_1∼ a_N , b_1∼ b_N , c_1∼ c_N ).
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