A directly pulsation power control strategy for single-phase power converters with E-cap free

In a single-phase power conversion system, bulky Electrolytic-capacitors (E-caps) are always used in voltage source converters at the DC-link to buffer the twice fundamental frequency pulsation power introduced by instantaneous unbalanced power between the AC and DC sides, and mitigate the harmonics from the AC side. However, the E-cap will cause harmful effects on the system, such as reducing the efficiency and shorting the lifetime of system. The E-cap free methods were identified as three types: reducing unbalance power, channeling new flowing path for the unbalanced power and compensating the unbalanced power inside of the converters. Based on this category, a directly pulsation power control strategy with differential structure was proposed, restraining the unbalanced power at the AC side by self-support, instead of transferring the unbalanced power to extra reliable energy storage components. Control functions for different kinds of harmonics were derived. Moreover, the control strategy for several modules in series for higher power was presented in this paper. The proposed directly pulsation power control strategy for single-phase converters (including rectifiers and inverters) could compensate the unbalanced power without extra hardware, reduce the flowing path of the pulsation power and improve the efficiency of the system. Experimental results are shown to verify the accuracy of the theoretical analysis.