Design and Efficiency Optimization of a High Step-Up Converter for DC Microgird

Since the excessive use of fossil energy has caused global warming and an energy crisis, clean energy development has gained much more attention. In order to reduce the impact of clean energy based distributed generation grid-connect, improving the conversion efficiency and reliable performance, DC microgrid plays an important role. However, the low output voltage of clean energy should be boosted to a suitable voltage level of the DC microgrid grid-connected. Therefore, a high step-up DC-DC converter using switched coupled inductor and passive clamp circuit is proposed. The switched coupled inductor technique is connected to the input and the output parts, and the voltage gain can be further improved by adjusting the turns ratio of the coupled inductor. In addition, by applying a passive clamp circuit, the energy stored in the leakage inductor is recycled, and the voltage spike on the power switch can be suppressed. Hence, the voltage stress on the switch is reduced, and the efficiency can be improved. The operating principles and steady-state performance in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are analyzed in detail. The operating mode is analyzed through the key waveforms and equivalent circuits. Considering the coupling coefficient has no significant effect on the voltage gain, the ideal voltage gain is (2+n)/(1−D) where n=ns/np. Under n=2 and D=0.6, the voltage gain can reach 10. Hence, the proposed converter can achieve high voltage gain. Meanwhile, the voltage stress and current stress of components are studied, including semiconductor devices and passive devices. Moreover, the parameters of the magnetizing inductor and capacitors are designed. The power loss is divided into four parts: power switch, diode, capacitor, and inductor losses. The theoretical efficiency and non-ideal voltage gain are obtained. Compared with the ideal and non-ideal voltage gains at the appropriate duty cycle, the effect of parasitic parameters of components is negligible. The proposed converter has higher voltage gain and efficiency, lower voltage stress of the power switch, and fewer components than the high step-up converter. A 40 V-input, 400 V-output, 250 W experimental prototype is built by choosing the proper value and type of components. Considering the inductor loss, the material of core and turns ratio are selected to achieve the highest efficiency. The measured voltage and current of components are consistent with the theoretical analysis. Also, the measured maximum and full-load efficiencies are 97.59% and 97.10%, respectively. Total power loss is 5.49 W at 250 W. The proposed converter has the following advantages. (1) The high voltage gain is obtained by switched coupled inductor, suitable for the DC microgrid grid-connected. (2) Through the experiment results, the low voltage stress of the power switch validates that the passive clamp circuit inhibits the voltage spike effectively. (3) The beneficial parameters are chosen to improve the efficiency, verifying the power loss analyses through the experiment. (4) Fewer components are required, which improves reliability. © 2023 Chinese Machine Press. All rights reserved.