INTERLEAVED SWITCHED-CAPACITOR BIDIRECTIONAL DC-DC CONVERTER WITH WIDE VOLTAGE-GAIN RANGE FOR ENERGY STORAGE SYSTEMS
Abstract:
In this paper, an interleaved switched-capacitor bidirectional DC-DC converter with a high step-up/step-down voltage gain is proposed. The interleaved structure is adopted in the low-voltage side of this converter to reduce the ripple of the current through the low-voltage side, and the series-connected structure is adopted in the high-voltage side to achieve the high step-up/step-down voltage gain. In addition, the bidirectional synchronous rectification operations are carried out without requiring any extra hardware, and the efficiency of the converter is improved. Furthermore, the operating principles, voltage and current stresses, and current ripple characteristics of the converter are analyzed. Finally, a 1kW prototype has been developed which verifies a wide voltage-gain range of this converter between the variable low-voltage side (50V-120V) and the constant high-voltage side (400V). The maximum efficiency of the converter is 95.21% in the step-up mode and 95.30% in the step-down mode. The experimental results also validate the feasibility and the effectiveness of the proposed topology.
PROPOSED SYSTEM:
The proposed interleaved switched-capacitor bidirectional DC-DC Converter is shown in Fig. 1. This converter is composed of four modules. C low is the energy storage/filter capacitor of the low-voltage side. Module 1 includes power semiconductors Q 1, Q 2, and energy storage/filter inductors L 1 , L 2 . In addition, L 1 –Q 1 and L 2 –Q 2 form the parallel structure of the low-voltage side. Module 2 is a switched-capacitor network, including switched-capacitor units C 1 –Q 3 , C 2 –Q 4 and C 3 . The interleaved structure is used in the low-voltage side of this converter. In this case, the duty cycles of Q 1 and Q 2 are the same, and the phase difference between the gate signals S 1 is 180°. The low-voltage side, Module 1, Module 2 and the high-voltage side form the bidirectional DC-DC converter with the structure of the low-voltage-side in parallel and the high-voltage-side in series. –Q 5 and S 2
EXISTING SYSTEM:
The non-isolated converters include the Cuk, Sepic/Zeta, coupled-inductor, conventional buck-boost, three-level, multi-level and switched-capacitor. Due to the cascaded configurations of two power stages, conversion efficiencies of Cuk and Sepic/Zeta are lower. Coupled-inductor converters can achieve a high voltage gain by adjusting the turns ratio of the coupled inductor, but the problem associated with the leakage inductor is still difficult to be solved and the converter’s power converting and transferring capabilities are limited by the capacity of the magnetic core. By utilizing a coupled-inductor, the Sepic converter has been modified, and a high efficiency and high voltage-gain bidirectional DC-DC converter with soft-switching was proposed in. But it requires extra active power semiconductors and capacitors. Conventional buck-boost converters are good candidates for low-voltage applications due to its high efficiency and low cost. Unfortunately, the drawbacks including the narrow voltage conversion range, the high voltage stress and extreme duty cycles of semiconductors make them not suitable for energy storage applications. Though the conventional two-phase interleaved bidirectional DC-DC converter can reduce low-voltage side current ripples, but this converter still has disadvantages including the narrow voltage conversion range and the high voltage stress for power semiconductors. The voltage stress of power semiconductors of the bidirectional three-level DC-DC converters is half that of the conventional two-phase interleaved bidirectional DC-DC converter, but its voltage-gain range is still narrow. Besides, the low-voltage and high-voltage side grounds of this converter are connected by a power semiconductor, the potential difference between the two grounds is a high frequency PWM voltage, which may result in more maintenance issues and EMI problems. The low-voltage and high-voltage sides of the bidirectional three-level DC-DC converter in share the common ground, but the voltage-gain of this converter is still limited. In addition, this converter requires the complicated control scheme to balance the flying-capacitor voltage. The converters in, and can achieve a high voltage gain, and the low voltage stress of power semiconductors.
CONCLUSIONS
In this paper, an interleaved switched-capacitor bidirectional DC-DC converter has been introduced. The proposed topology can benefit from high step-up/step-down ratio, a wide voltage-gain range and avoiding of the extreme duty cycles. In addition, this converter has the advantages of the low voltage stress of power semiconductors and capacitors, and low current ripples in the low-voltage side. Besides, the slave active power semiconductors allow ZVS turn-on and turn-off, and the efficiency of the converter is improved. The capacitor voltages and the inductor currents can be easily balanced due to the self-balance function. The proposed bidirectional DC-DC converter has good dynamic and steady-state performance and is suitable for the power interface between the low-voltage battery pack and the high-voltage DC bus for various new energy storage systems.
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