A Single Phase, Single Stage AC-DC Multilevel LLC Resonant Converter With Power Factor Correction

Abstract

Single stage LLC resonant converters with inherent power factor correction are getting popularity in AC-DC converters due to its reduced size and weight. However, single stage topologies are usually less efficient in regulating the dc bus capacitor voltage pertaining to line and load transients. This paper proposes a multi-level flying capacitor based single stage AC-DC LLC topology to address the issue of voltage balancing of dc-bus capacitor and to reduce the voltage stress of the switching devices. The proposed three-level inverter topology guarantees zero voltage switching, less circulating currents, reduced switching stress and losses. The converter uses bridgeless rectification scheme for better efficiency and the power factor is made nearly unity by operating the source-side inductor in discontinuous current conduction. Variable switching frequency control is used to regulate the output voltage of the converter and pulse width modulation is used to control the dc-bus voltage. This dual control scheme is very effective to keep the dc-bus voltage nearly constant over a wide range of line and load variations. The proposed topology and control scheme have been validated by hardware results on a 250W resistive load.

A hybrid bridgeless AC‐DC converter topology

“…A comparison study between the proposed bridgeless ac-dc single-stage topology, shown in Figure 1, and the three topologies proposed in articles [20][21][22] is summarized in Table 1. This comparison highlights the strengths of the proposed converter.…”

“…17,18 To overcome this problem, bridgeless ac-dc single-stage PFC topologies are proposed. 17,[19][20][21][22][23][24][25][26] The proposed bridgeless ac-dc single-stage PFC rectifier in Das et al 20 is based on an isolated single active bridge (SAB) converter. This converter features controlled dc-bus voltage with a unity power factor and acceptable input current THD.…”

A Review on State-of-the-Art Power Converters: Bidirectional, Resonant, Multilevel Converters and Their Derivatives

“…This control technique works well to maintain almost constant DC-bus voltage throughout a wide range of line and load variations. Figure 36 shows the three-level flying capacitor LLC resonant converter [149]. The study by [150] presented a five-level cascaded LLC resonant converter; the design and analysis of the system were presented for use in energy storage systems (ESSs) or grid-connected applications.…”

Design Methodology and Analysis of Five-Level LLC Resonant Converter for Battery Chargers

“…The researcher also analyzed the wide-adjustable-range LLC resonant converter used in lithium-ion battery LIB charger of a plug-in hybrid EV system PHEV [31]. Different scholars [32][33][34][35][36] have also proposed a hybrid of LLC converter with a three-level conversion approach. MLIs are used to alleviate voltage stress experienced by switching devices; they are also used to increase the power range of LLC resonant converter as reported by [37,38].…”

“…As mentioned earlier, the conventional topologies for realizing resonant converters are half-bridge and full-bridge, and multilevel inverters are not favorable for high-frequency resonant inverters since modelling them for control design is difficult, particularly when using high-frequency switching modulation approaches. To eliminate the drawbacks associated with half-bridge [6], full-bridge [40], phase-shifted full-bridge [41], and threelevel [36] inverters integrated with resonant tank network, a five level multilevel inverter is introduced in this paper.…”