Full-bridge Zero-current Switching Research Articles

FB-ZCS DC–DC Converter With Dual-Capacitor Resonant Circuit for Renewable Energy Integration With MVDC Grids

Full-bridge zero-current-switching (FB-ZCS) dc–dc converters realize quasi-resonant soft-switching and smooth current commutation by utilizing the leakage inductance of high-frequency transformer and a resonant capacitor. The following two types of resonant capacitor configurations are proposed in the literature: First, shunt-connected across the transformer-secondary and, second, series-connected with the transformer-primary. Shunt-connected capacitor has the drawbacks of storing full-load-rated resonant energy irrespective of converter loading. This results in large duty-cycle loss and consequently regulation loss at light-loads. Series-connected capacitor addresses this issue but suffers from higher peak-voltage stress across components and insufficient voltage for resonance at light-loads. To address these limitations, a dual-capacitor resonant circuit is proposed in this article. Series-capacitor facilitates current-adaptive resonant energy storage and shunt-capacitor is designed only for a fraction of full-load-rated resonant energy, which lowers the duty-cycle loss and supports soft-switching at light-loads. This combination also reduces the series-capacitor voltage required for resonance, thereby reducing the peak-voltage stress. Steady-state analysis of converter operation is presented and the advantages over existing converters are demonstrated through simulations for medium-voltage dc application. Experimental results from a scaled-down prototype are presented to validate the proposed converter.

IPOP-Connected FB-ZCS DC–DC Converter Modules for Renewable Energy Integration With Medium-Voltage DC Grids

This paper presents a dc–dc input-parallel output-parallel (IPOP) converter configuration for renewable energy integration with medium-voltage dc grids. A full-bridge zero-current-switching (FB-ZCS) converter with voltage-doubler output is proposed as the fundamental module. To achieve smooth current commutation and ZCS, the leakage inductance of transformer and a resonant capacitor across its secondary are utilized. This resonant capacitor is always charged to its full-rated capacity irrespective of converter loading and requires a dedicated charging interval resulting in duty-cycle loss. For a given leakage inductance, a large resonant capacitor is required for higher current ratings. With a single-centralized converter, these operational and design constraints result in significant duty-cycle loss, restricting the operation range. This paper proposes an IPOP configuration for high-power applications. Phase shedding at reduced loading ensures that individual modules are operated optimally. Input inductance requirement in modules is reduced due to interleaving of the input current. Additionally, voltage stress across converter components and input current ripple are reduced by 50% in the proposed converter modules. Steady-state operation, modeling, current-sharing control, start-up, and shutdown of modules in the IPOP configuration are demonstrated using simulations. Experimental results on a scaled-down prototype are presented to validate its operation.

Full-Bridge ZCS-Converter-Based High-Gain Modular DC-DC Converter for PV Integration With Medium-Voltage DC Grids

This paper presents a high-gain modular input-parallel output-series dc-dc converter for photovoltaic integration with medium-voltage dc grids. A new full-bridge zero-current-switching (FB-ZCS) converter proposed in this paper is used as a fundamental building block. Existing FB-ZCS converters utilize transformer leakage inductance and a shunt-connected resonant capacitor for achieving smooth resonant current commutation and ZCS. The shunt-connected capacitor requires dedicated charging interval in every switching cycle and stores full-load-rated resonant energy at all load/input conditions, resulting in significant duty-cycle loss. Moreover, it suffers from energy leakage through transformer winding and requires overrating. All these factors adversely impact the operation range of the converter, which is important for achieving a wide maximum power point tracking range. Novel improvements in the proposed converter include minimization of duty-cycle loss and resonant capacitor leakage and the realization of the current-adaptive resonant energy storage mechanism, without using additional switches or auxiliary circuits. Operation of the proposed converter is presented and validated with simulation and experimental results.

Buck-current-fed zero current switching converter for high voltage coupled cavity

This paper presents a design of buck-current-fed full-bridge zero current switching converters which are suitable for high-power high-voltage DC applications. This study shows the capability of incorporating the step-up transformer parasitic components to get the zero current turn-off characteristics for full-bridge switches. The buck stage of the converter uses pulse-width-modulation control to regulate the output voltage and the full-bridge stage operates at a constant on time mode to implement soft-switching commutations. In this study, the converter model is derived, and this model is implemented in an IsSpice circuit, which can reveal the transient characteristics of the converter. Steady state analysis of the converter is also presented. Finally, the simulation results of this converter for the application of coupled cavity traveling wave tube are given and major design issues are discussed.

Steady-state analysis of full-bridge zero-current switching converter

A steady-state analysis of the full-bridge zero-current-switched (FB-ZCS) pulsewidth modulation (PWM) converter is presented. The FB-ZCS is fully able to incorporate parasitic parameters, and zero-current turn-off characteristics. The converter utilises the parasitic parameters of components, particularly for high-voltage transformers, and employs fixed frequency phase-shift control to implement soft-switching commutations.