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A totem-pole bridgeless boost converter is one of the most promising topologies for the power factor correction (PFC) stage in high-power applications due to its high efficiency and small number of components. However, due to the totem-pole structure of the field-effect transistor (FET), very high switching loss occurs via the reverse recovery current of the body diode. To solve these problems, critical mode (CRM) control is a good solution to achieve the valley switching technique. With valley switching of CRM control, the switching loss decreases drastically with decreasing turn-on voltage. But, although the CRM control enables valley switching, it is hard to make an exact valley switching control with general zero-voltage detection circuits. In addition, when a frequency limitation scheme is applied to prevent a very high frequency, the switch can operate with hard switching at the boundary of the frequency limitation. Furthermore, the CRM boost PFC has a low PF and high total harmonic distortion (THD) under light-load conditions due to the large negative current resulting from resonance between the inductor and parasitic capacitance. It becomes worse at near-zero input voltage since the resonance current becomes larger near zero-input voltage. Therefore, in this paper, a totem-pole bridgeless boost PFC converter with high efficiency, high PF, and low THD is developed using TMS320F28377 by Texas Instruments. Based on the basic digital structure of the totem-pole bridgeless converter, the proposed controls help with exact valley switching, PF and THD improvement, and frequency limitation. The prototype converter is verified using 90–264 VAC input voltages and 450 V/3.3 kW output specifications. [ABSTRACT FROM AUTHOR]

• Tellegen's theorem is introduced into the LCC-HVDC receiving-end AC power grid, and the instantaneous quasi-power characteristics are derived. • The quasi-power difference differential is defined to characterize differences between the internal and external faults and solve the problem caused by the distributed capacitance and reactive currents crossing through the transmission line. • The proposed pilot protection is immune to the control strategy of the inverter, commutation failure, receiving system strength and other factors. • The proposed protection can detect the fault within 5 ms. Affected by the control strategy and nonlinear characteristics of the inverter station, the traditional pilot protection relays employed in AC transmission lines do not perform well or even fail at the receiving end of the line commutated converter-based high-voltage direct-current system, thereby posing concealed threats to the security of the system. Leveraging the universality of Tellegen's theorem, this paper introduces the theorem to the realm of the AC-DC hybrid system. The characteristics of quasi-power difference under various conditions are analyzed, and a pilot protection criterion is proposed based on the quasi-power difference differential value. The AC grid model of the receiving end of the Tian-Zhong HVDC project in China is established in PSCAD/EMTDC to carry out simulation and performance analysis for the proposed protection under different fault cases. Furthermore, the proposed protection criterion undergoes validation using on-site fault recording data. The test results show that the proposed method is immune to the inverter control strategies, commutation failure, receiving system strength, and other factors. The new method is more adaptive to the AC system connected to the inverter station. [ABSTRACT FROM AUTHOR]