Towards high power-density, high efficiency and high reliability single-phase power conversion

Abstract

Adoption of bulky electrolytic capacitors (E-caps) is a crucial obstacle for single-phase power-factor-correction (PFC) rectifiers toward high power density and high reliability. Active pulsating-power-buffering (PPB) is an effective technique to reduce the energy storage requirement, thereby eliminating the usage of E-caps. Existing active PPB solutions, however, generally suffer from some issues or limitations, such as (i) extra power electronics are required to form PPB active filter; (ii) high voltage stresses for semiconductors and (iii) limited output dc voltage range. These issues or limitations inevitably lead to an increased system cost, degraded energy efficiency, and limited application. In this thesis, the active PPB technique is further explored. Four PFC circuits without E-caps are proposed, and a complementary voltage sensorless control method is also proposed for these circuits. The contributions are summarized as follow: 1. Proposed a single-phase AC/DC converter without additional active switches and its control method. The achievable efficiency of the circuit is even higher than that achievable withwith the H-bridge converter in some operation range. 2. Proposed a two-switch single-phase buck-boost PFC rectifier as well as its closed-loop control method. This rectifier can achieve good PFC, output voltage regulation and active PPB, all in a single stage. 3. Proposed a single-phase three-level flying-capacitor buck-boost PFC rectifier and its control method. The flying capacitor serves dual purposes of clamping the voltage stresses of all power devices and operating as a PPB capacitor. By virtue of the three-level configuration, the voltage stress and the inductance requirement are also reduced significantly. 4. Proposed a single-phase three-level flying-capacitor buck PFC rectifier and its control method. The proposed solution is found to have lower voltage and current stresses, reduced magnetic and capacitive footprints, as well as a unity power factor (PF) and a lower total harmonic distortion (THD), as compared to those of a conventional buck PFC converter. 5. Proposed a voltage sensorless control method for a type of active PPB-based single-phase rectifier featuring only one inductor (applicable for the rectifiers in contributions 2, 3, and 4). Three voltage sensors together with their associated isolated power supplies are saved from the circuit with this control. Experiments have been conducted to confirm the feasibility of the proposed circuits and control methods.