A novel pulse frequency and phase shift hybrid modulated dual-output dc-dc converter is proposed in this paper. The proposed converter is composed of hybrid modulation of an input-parallel-output-series LLC resonant converter and a phase shift full bridge (PSFB) converter. The output voltage of the LLC resonant converter is modulated by the switching frequency, whereas the output voltage of the PSFB converter is modulated by the phase angle; therefore, the two output voltages are regulated independently and free from cross regulation. The series inductor of the PSFB converter does not need to be specially designed to help achieving the soft switching operation, and the duty cycle loss could be mitigated. Zero-voltage switching can be achieved on the power switches in the whole load range. Finally, a 1.2-kW 400-input 200-400-V and 48-V output prototype is built and tested to verify the effectiveness of the proposed converter.

Voltage source inverters (VSIs) are usually used for all kinds of distributed generation interfaces in a microgrid. It is the microgrid's superiority to power the local loads continuously when the utility fails. When in islanded mode, the voltage and frequency of the microgrid are determined by the VSIs; therefore the power quality can be deteriorated under unbalanced and non‐linear loads. A voltage unbalance and harmonics compensation strategy for the VSIs in islanded microgrid is proposed in this study. This method is implemented in a single synchronous reference frame (SRF) and is responsible for both the voltage unbalance and harmonic compensation. Furthermore, the virtual impedance loop is modified to improve the compensation effect. The impedance model of the VSI is built to explain the compensation ability of the proposed strategy. The whole control system mainly includes power droop controllers, a modified virtual impedance loop and inner SRF‐based voltage unbalance and harmonics compensators. The proposed strategy is demonstrated in detail and validated with simulations and experiments.

In this paper, a voltage multiplier cell is inserted in the conventional boost converter operated in continuous conduction mode (CCM) to provide another design freedom for the voltage-gain extension. Thus, the voltage conversion ratio is enlarged and the narrow turn-OFF period is avoided in the high step-up applications. Furthermore, the voltage multiplier cell makes the voltage stress of all the power devices lower than the high output voltage. As a result, the low-voltage-rated power devices can be employed to reduce the conduction losses and to improve the power device reliability. Moreover, zero-voltage switching soft-switching operation is achieved for the power MOSFETs in the whole-switching transition. Zero-current switching turn-OFF condition is provided for the diodes. Therefore, the power device switching losses and the diode reverse-recovery losses are minimized greatly. In addition, the input current ripple is reduced due to the CCM operation compared with most of the published single-stage single-phase high step-up converters, which makes it more advantageous in the hybrid electric vehicles and the fuel-cell power conversion systems. Finally, the experimental results from a 500-W, 36-380-V prototype are provided to validate the effectiveness of the proposed converter.

In this paper, a new voltage balancing strategy based on improved carrier-phase-shifted pulsewidth modulation (CPS-PWM) scheme and fundamental frequency sorting algorithm (FFSA) is proposed. FFSA is a salient method which sorts the capacitor voltages at fundamental frequency and utilizes the different charging ability of driving signals to converge the capacitor voltages. Unfortunately, under the CPS-PWM scheme with high carrier frequency, 250 Hz or higher, FFSA cannot bring the capacitor voltage to the nominal value once the unbalance occurs, because there is a little difference remaining in the driving signal's charging ability. To avoid this disadvantage, an improved CPS-PWM scheme is proposed. In this scheme, driving signals with proper phase angle differences are selected to be dealt with logic and/or processing according to the sorting result of FFSA. With the logic processing, new driving signals with obviously different charging abilities are synthesized, which are assigned to the corresponding unbalanced submodules to achieve the balance of capacitor voltages. And several regions for logic processing are set up, where the proper phase angle difference is selected for each region in order to both guarantee the convergence speed and avoid the voltage oscillations. With the proposed scheme, FFSA can be adopted under CPS-PWM with high carrier frequency. Moreover, the merits of FFSA are inherited, such as the reduced computational burden and the elimination of arm current detection. Performance and effectiveness of the proposed strategy are validated by both simulations and experimental results.

The diagnosis of open-circuit faults is required for the reliability of modular multilevel converters (MMC) and the complex operating environment of MMC may cause missing data and external noise in signal detections, where some of the present open-circuit fault detection methods can be disabled. This article proposed a machine learning (ML) diagnosis strategy for open-circuit faults in MMC based on extreme gradient boosting (XG-Boost). In this method, after data processing, the data segments composed of real-time capacitance voltage and current data are input into the trained XG-Boost multiclassification model for fault diagnosis without manually setting the empirical threshold, as is required in traditional change-of-rate-of-voltage-based diagnosis methods. This method has excellent robustness against external noise and missing data while better accuracy, higher speed, and lower real-time calculation cost than existing ML-based methods are achieved. The effectiveness of the proposed method is verified by experiment results. It can diagnose the fault within 20 ms with accuracy as high as 99.6%, even under the interference of Gaussian noise and the capacitor voltage data missing.

This paper proposes a novel single-phase single-stage ac-dc converter with high-frequency isolation and power factor correction. Unlike the two-stage ac-dc converters, the high-frequency pulsating voltage is obtained directly from the power factor correction semistage and is applied directly to the dc-dc semistage. The proposed topology is designed to be operated in the continuous conduction mode (CCM), and therefore, there is no need for additional input filter. In addition, the interleaving operation helps reducing the current stress and gets a better electro-magnetic interference performance. Moreover, all of the power switches in the proposed topology can achieve soft-switching commutation. Furthermore, the intermediate dc-link capacitor is no longer directly connected to the dc-dc stage and the capacitance can be reduced greatly; therefore, the bulk capacitor is replaced by a film capacitor. Frequency characteristics and time-domain analysis of the LLC resonant tank is presented in this paper to analyze the characteristics of the proposed converter. Finally, a prototype that converts universal input voltage ranging from 110 to 220 V into 400-V dc output was built and tested to verify the analysis.