The five-level active neutral-point-clamped (5L-ANPC) converter has a great application potential in high power variable-frequency drives (VFDs) with high and medium voltage. However, the traditional method for capacitor voltage buildup is not applicable to the capacitors inside the back-to-back (B2B) 5L-ANPC converter. To solve the problem, the topological features of the B2B-5L-ANPC converter are fully analyzed, and a capacitor voltage pre-charge strategy for this converter is also proposed. With this strategy, all the capacitors in the converter can be charged by controlling the on and off states of switch tubes in the bridge arm, no additional hardware is needed. Moreover, the structural features of the voltage booster circuit were examined in four stages, and used to derive the capacitor voltage buildup formula in each stage. In addition, the relationship between voltage buildup rate, equivalent pre-charge resistor and capacity of capacitor is identified. Finally, Simulation results from a B2B-5L-ANPC simulation model which is constructed according to the actual system parameters and experimental results from a scaled-down prototype are provided to support the proposed control strategy.

To improve the power factor and reliability for medium/high-power supply, a three-phase single-stage ac-dc converter based on magnetic-combination transformer with power factor correction (PFC) function is presented in this paper. According to the three-phase instantaneous power balance principle and the concept of the magnetic-flux superposition, a novel magnetic-combination transformer is proposed, which can make three-phase symmetrically and sinusoidally fluctuant power add to be constant. Therefore, the induced voltage of the secondary winding is constant. To realize sinusoidally fluctuant power in the input stage, dc-link filter capacitance can be reduced to a several-microfarad level. Single-stage PFC function, no electrolytic capacitor, and constant output voltage can be realized in the converter. The principle and the structure of the novel magnetic-combination transformer are analyzed in detail in this paper. Simulation and experimental results are presented to verify the feasibility of the proposed converter.

Distribution Automation is one of the most important parts of the construction of Smart Grid. And the related standards are important for Smart Grid standard system. Modern power distribution network, which has three features including network grid, multi-connecting power supply and distribution automation, will strengthen the network connection. It improves the power supply service that less time is needed to recover when breakdown happens. Radar reflection principle is used for the strategy of load-transfer among main stations of Distribution automation in Pudong area, which consists of load shedding plan, checking method of topological power flow and searching the path of power supply. Therefore, it is possible to recover from complex breakdown nearby and separately, which ensures the distribution automation system work more steadily and reliably.

In order to accurately locate the open-circuit fault of power tube for three-phase PWM rectifier under the grid-voltage sensorless control strategy, an open-circuit fault diagnosis algorithm based on phase angle partitions of the current and voltage is proposed. To improve dynamic response for the system, predictive current control is implemented. The real-time change rate of the grid-current phase angle is utilized to determine whether a fault occurs. Based on the zero value platform in the grid-side distortion current generated by open-circuit faults, the corresponding phase angles for the grid current and the grid voltage are partitioned to locate the fault tubes. In a grid voltage sensorless control system, the grid voltage information obtained by the voltage observer and phase-locked loop can be susceptible to distortion or interference. To enhance the accuracy of phase-locked angle, a double generalized second-order integrator is used. The proposed open-circuit fault detection method can realize rapid diagnosis and location for single and double power tubes under grid-voltage sensorless predictive current control. Finally, experimental results are presented to verify the feasibility of the diagnosis method.