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.

This paper proposes a hybrid model predictive control (HMPC) for a modified modular multilevel switch-mode power amplifier (M3-SMPA).The M3-SMPA consists of two parts connected in series including modular multilevel converter (MMC) and full-bridge converter (FBC). Different from available MPC methods that only apply either finite control set MPC (FMPC) or modulated MPC (MMPC), the proposed HMPC method synthesizes the merits of both FMPC and MMPC on different time scales. Firstly, the optimal control option (CO) for MMC is calculated by FMPC with the multiple control objectives including output voltage control, circulating current control, and submodules (SMs) capacitor voltages balance control. Then based on the above optimal CO, the optimal duty cycle for FBC is calculated by MMPC with a single objective of output voltage control. In this case, the FMPC achieves the multi-objective control of MMC while the MMPC eliminates the tracking error of output voltage using FBC with a fixed switching frequency. Furthermore, a circulating current injection method is presented to balance the SMs capacitor voltages and an improved adjacent search (IAS) method is introduced to reduce the evaluated COs for MMC in each control period. The effect of DC-link voltage configuration for FBC on output steady-state performance is also analyzed. Finally, the effectiveness of the proposed HMPC method is verified by experimental results.Index Terms-hybrid model predictive control (HMPC), modified modular multilevel converter (M3C), switch-mode power amplifier, finite control set model predictive control (FMPC), modulated model predictive control (MMPC), improved adjacent search 

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.

Digital current control method is the mainstream method for high-power DC/DC converters. However, digital controllers require additional filters for noise suppression to ensure their proper operation in the complicated electromagnetic environment. The filtering processes coupled with the inherent time delays of digital systems significantly degrade dynamic performance. Thus, steady-state performance is improved at cost of dynamic performance in conventional current control. To solve the problems, this paper establishes a deadbeat average control model based on application of the oversampling technique for phase-shifted full-bridge (PS-FB) DC/DC converter and proposes a predictive deadbeat average model control method by incorporating predictive control into the proposed control model. Simulation and experimental results verify the effectiveness of the proposed control method in mitigating the contradiction between steady-state performance and dynamic performance in the digital system.

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.