An Improved Modulation Strategy Combining Phase Shifted PWM and Phase Disposition PWM for Cascaded H-Bridge Inverters

Abstract: Multilevel modulation strategy is an important factor affecting the output performance of multilevel converters. In this paper, the relationship between phase-shifted pulse width modulation (PWM) and phase disposition PWM is analyzed, and then an improved hybrid modulation strategy is proposed for cascaded H-bridge. In addition, the implementation method of multilevel discontinuous modulation for an improved modulation strategy is described. The new modulation strategy is optimized to increase the DC link voltage utilization and further improvement in output harmonics by the injection of a common voltage into the reference. Simulation and experiment verify the effectiveness of the proposed modulation strategy

Optimal design of high frequency high efficiency and high‐power density DC–DC power module based on GaN

Abstract This paper develops a railway power module with wide range voltage (dc 60—dc 160 V) input and constant voltage output (24 V/10 A) . The power module adopts a two‐stage topology structure to realize voltage conversion. Use the most advanced GaN (gallium nitride) as the main power switching devices. The first stage circuit architecture uses a two‐phase interleaved buck converter convert the wide range input voltage into a constant intermediate bus voltage (48 V) through closed‐loop control, and then the LLC resonant converter converts the intermediate bus voltage (dc 48 V) into a constant output voltage (dc 24 V) through open‐loop control, and realize the primary side and secondary side dc 3000 V electrical isolation. This article from the circuit topology, the power devices selection, buck converter magnetic integrated coupling inductance design, planar magnetic integration LLC resonant transformer optimization design has carried on the detailed discuss and analysis. All circuits are integrated in a standard quarter power brick module, the final prototype can reach 96.1% peak efficiency, the power density can reach 185 W/in.3

Power Control and Fault Ride-Through Capability Analysis of Cascaded Star-Connected SVG under Asymmetrical Voltage Conditions

The cascaded H-bridge static var generator (SVG) has been employed to provide reactive power and regulate grid voltages for many years because of its good modularity, easy scalability, and improved harmonic performance. A novel cluster-balancing power control method combining negative-sequence currents and zero-sequence voltage is proposed to redistribute the unbalanced active powers and eliminate the power oscillation under asymmetrical conditions. Simultaneously, the dynamic performance of the SVG power balance control can be improved under asymmetrical conditions with the zero-sequence voltage expression derived in this paper. On the basis of the proposed method, the fault ride through capability of star-connected SVG under asymmetrical conditions is compared among active power oscillation elimination (APOE), reactive power oscillation elimination (RPOE), and balanced positive sequence current (BPSC) injection references calculation strategies from the perspective of the zero-sequence voltage, maximum phase voltage, and maximum phase current. The method provides the theoretical reference for power control under asymmetric conditions and the analysis results show that under asymmetrical conditions, the current of BPSC is minimal and symmetrical, while the RPOE has the least voltage and no zero- sequence voltage needs to be injected. Finally, the results of simulation and experiment have been given to verify the theoretical studies