Analysis and implementation of a three‐level hybrid dc–dc converter with the balanced capacitor voltages

Abstract

In this study, a three-level hybrid dc/dc converter by integrating the full-bridge circuit, resonant circuit and threelevel flying capacitor circuit is presented to achieve the main advantages of low-voltage stress of power devices, low circulating loss, low-voltage ringing on the rectifier diodes and low-output filter inductor for medium-voltage dc-based systems. Two full-bridge circuits are connected in series to effectively reduce the voltage stress of switches. Half-bridge resonant circuit shared the lagging-leg switches of full-bridge circuit is used and operated at fixed switching frequency to extend the zero-voltage switching (ZVS) range from low load to full load. Thus, the drawback of narrow ZVS range in the conventional full-bridge converter is improved. A flying capacitor is adopted to automatically balance input split capacitor voltages in each switching cycle without any additional active components or complexity control scheme. The circulating loss in the full-bridge circuit is reduced to zero by parallel connection of outputs of full-bridge circuit and half-bridge resonant circuits. Finally, the theoretical analysis and performance of the proposed converter are verified by the experiments with a 1.92 kW prototype circuit.

Three‐level dual‐buck voltage balancer with active output voltagesbalancing

“…The three-level topology is widely used in high voltage and highpower applications, such as high DC power converters, high power inverter and distributed energy systems [1][2][3][4][5][6][7][8][9][10][11][12][13], and so on. However, if the input voltage of the three-level topology is not balanced, the bad effects on three-level states and the quality of the output voltage/current will appear.…”

“…To avoid the problems, many control methods have been studied, such as a ZVS PWM strategy [1], a hysteresis comparator in regulating the DC-link capacitor voltages [4], adjusting the proportion of the redundant small vectors duration in SVPWM [5], a compensating scheme based on a current compensation method [6], the LMSVM technique [7], and the nearest three-vector scheme [8]. The problem can also be overcome by the modulation with extending the regions around zero voltage [9], the external balancing circuit [10], and a flying capacitor balancing input split capacitor voltages [11].…”

Wide Load Range Capacitor Clamped ZVZCS Half Bridge Three-Level DC-DC Converter with Two Unsymmetrical Bi-directional Switches

“…The most outstanding attribute of TLDC is reduced voltage stress of the primary switches, and both dynamic and static voltages on the main switches can be confined below V in /2 by the clamping devices, such as clamping diodes or capacitors. After diode-clamped TLDC was proposed in 1992, several good studies on this topic have been carried out, which are new topologies, wide load range soft-switching techniques, reduced volume of passive components methods, and new control strategies [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Several TLDCs were proposed in Reference [5], and most existing TLDCs are invented based on these topologies.…”

“…In Reference [7], a passive snubber is series-connected with the primary coil of the transformer to generate reset voltage of the primary current, and two diodes are used to prevent a negative primary current during the free-wheeling stages. Some other new TLDCs were reported in References [8][9][10][11][12][13][14], which have different attractive characteristics. To reduce the volume of the passive filter, lots of TLDCs with TL secondary-rectified voltage waveforms were proposed.…”

Periodically Swapping Modulation (PSM) Strategy for Three-Level (TL) DC/DC Converters With Balanced Switch Currents

“…Many studies have been carried recently on the TL DC/DC converters, which mainly focus on the topics of extending the soft switching range [17], [18], reducing the circulating currents [19], and balancing the voltages on the input capacitors [20], [21]. However, until now there are few studies discussing about such current imbalance of the primary power switches in the TL DC/DC converters under the conventional asymmetrical modulation strategy, which would affect the reliability of the converter by causing the power loss [23].…”