No abstract

In this paper, an improved time‐domain analytical method for LLC resonant converters is proposed. Unlike traditional time‐domain analytical methods, the resonant current in the dead time is derived by considering the equivalent capacitances of the switching devices and the transformer. The equivalent output capacitance of the primary‐side switch is calculated by using a two‐segment fitting approach. The equivalent capacitance of the transformer is calculated by using the six‐capacitor model. The current increment method is used to calculate the initial value of the magnetizing current and to determine the numerical calculation conditions for the proposed time‐domain expressions. Finally, the dead time ranges for zero‐voltage switching of the converter are derived based on the improved time‐domain method. Experiments were carried out with a 10 kW LLC resonant converter. The lower limit of the dead time calculated with the proposed method is closer to the experimental results than the values of two conventional methods.

Purpose This paper aims to study a multi-level reinjection current source converter (MLR-CSC) that adds attracting properties such as the self-commutation and pulse multiplication to the thyristor converter, which is of great significance for increasing the device capacity and reducing current harmonics on the grid side. Particularly, designing advantageous driving methods of the reinjection circuit is a critical issue that impacts the harmonic reduction and operation reliability of the MLR-CSC. Design/methodology/approach To deal with the mentioned issue, this paper takes the five-level reinjection current source converter (FLR-CSC), which is a type of the MLR-CSC, as the research object. Then, a method that can fully use combinations of five-level reinjection switching functions based on the concept of decomposition and recombination is proposed. It is worthy to mention that the proposed method can be easily extended to other multi-level reinjection circuits. Moreover, the working principle of the three-phase bridge circuit based on semi-controlled thyristors in the FLR-CSC that can achieve the four-quadrant power conversion is analyzed in detail. Findings Finally, the simulation and experimental results of FLR-CSC verify the effectiveness of the proposed reinjection circuit driving method and the operating principle of four-quadrant power conversion in this paper. Originality/value The outstanding features of the proposed driving method for FLR-CSC in this paper include combinations of reinjection switching functions that are fully exploited through three simple steps and can be conveniently extended to other multi-level reinjection circuits.