LLC resonant converters, generally adopting frequency modulation control, can hardly achieve high efficiency under both heavy and light load conditions. Especially under light load conditions, the high‐switching frequency seriously degrades converter's efficiency. This study propose a new pulse‐width modulation (PWM) control strategy for LLC resonant converters under light load applications on the premise of no change in the main circuit structure. The voltage gain of the converter is regulated by varying duty ratio instead of increasing switching frequency and therefore zero‐current switching for rectifier diodes can be realised under light load conditions. With the proposed PWM control strategy, the gain is not affected by the load variations and an optimal design of the magnetic components is possible, therefore the efficiency is further improved by reducing both the switching losses and the losses in magnetic components. Experimental results demonstrate the effectiveness of the proposed PWM strategy by increasing the efficiency of LCC resonant converter, especially under light load conditions.

Active power filters (APFs) with repetitive control (RC) could compensate for the harmonics. However, there are some problems in IGBT-380V-APFs with RC, such as the adaptability of grid frequency varying because of the noninteger value of RC parameters. SiC- mosfet s that could reach high switching frequency provide a new way to increase the compensation accuracy and the frequency adaptability for 380V/APFs. In this article, a novel frequency adaptive fast repetitive control (FAFRC) for APF with SiC- mosfet inverter to achieve optimal performance in variable frequency girds through changing RC order N was proposed. Taking the advantage of the high switching and sampling frequency of SiC-APF, the control method proposed could compensate for the harmonics more accurately with an integer RC order N . The control method with 50 kHz switching and the sampling frequency is described, designed, and verified experimentally in a two-level 380V/75A APF prototype made up of SiC- mosfet s, which volume is 37L that 66% of IGBT-APFs. The results obtained that 380V/75A-SiC-APFs with the control method proposed have a high compensation accuracy (THD<5%) with the grid frequency variations.

Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) has been seen as one of the most potential power semiconductor devices since it's commercialized. However, the advantages of fast switching speed with low conduction resistance always have to compromise to the fast switching on evoked overvoltage. Though it has been realized that overvoltage problem arises from the joint effect of fast switch speed and parasitics, there is a lack of ways for quantitative analysis. This paper proposes a reliable circuit model based on which a quantitative way to analyze the cause of overvoltage and find optimized parameters to suppress it is detailed. A normalized method is adopted to make the analysis more general, and the voltage and current stress determined Safe Operation Area during the switching on process under the constraint of maximum overvoltage is detailed. The analysis is verified by a double pulse test experiment with the calculated and measured maximum overvoltage matching very well. The analysis can help to choose reasonable turn on speed and power loop parasitic inductance before the PCB manufacture with an acceptable maximum overvoltage guaranteed.

LCC resonant converters have been widely adopted to achieve high power density and high efficiency. Due to high switching frequency and large reactive power in the resonant tank, the efficiency of LCC converters at light load decreases dramatically. Burst mode, which is commonly used in dc–dc converters to improve efficiency at light load, has not been applied to LCC resonant converters due to the oscillation of resonant tank during the burst off -time of burst mode. In this article, a simplified state model, which has only two state variables that can easily describe its state trajectory in the state plane, is proposed for LCC resonant converters with a capacitive output filter. Then, optimal state trajectory control of LCC converters for burst mode is proposed based on the state model, which can eliminate the resonance during the burst off -time. In addition, the transition from start-up mode to burst mode is proposed based on state trajectory control, which can complete this transition in one switching cycle. Finally, the proposed optimal trajectory control in burst mode is verified by an LCC converter prototype.

Fast and accurate optimization of the dynamic response is very important for an LCC resonant converter. The trajectory control is an effective way to achieve these goals. However, the model of the LCC resonant converter is generally too complex to get the target steady-state operation frequency and trajectory online and in real time with the common controllers. In this article, a fast solution can be obtained by adopting the proposed two-point solution method. A simplified steady-state trajectory model is also established, which is the solution object of the two-point solution method. When the necessary parameters are acquired, the target state trajectory and operation parameters, e.g., frequency, can be obtained quickly and accurately. Furthermore, the fast and accurate control strategy based on the simplified state trajectory and the two-point solution method is proposed to realize control of the LCC converter. The experiments are performed to verify the proposed control strategy. During the load transient, compared with the conventional proportional–integral control, the voltage variation and the response time are improved by more than 80%, respectively, and the two-point solution method can be finished within 2.3 μs by the controller. The fast response with a very small voltage variation is realized by the proposed control strategy.