Bridgeless rectifiers are widely used in many applications due to a unity power factor, lower conduction loss and high efficiency, which does not need bidirectional energy transmission. In this case, the potential failures are threatening the reliability of these converters in critical applications such as power supply and electric motor driver. In this paper, open circuit fault is analyzed, taking a three-phase bridgeless as an example. Interference on both the input and output side are considered. Then, the fault diagnosis method including detection and location, and fault tolerance through additional switches are proposed. At last, simulation and experiments based on the hardware in loop technology are used to validate the feasibility of fault diagnosis and fault tolerance methodology.

This paper presents an evaluation and comprehensive comparison for the topologies which are applied to the front stage of transformer-less cascaded multilevel converter (TCMC). The topologies investigated are targeted at the bidirectional cascaded H-bridge rectifier and three unidirectional rectifiers, including the diode H-bridge cascaded boost rectifier, cascaded bridgeless rectifier and cascaded VIENNA rectifier. First, the operation principles of the unidirectional rectifiers are discussed. Then the performances of these topologies such as power losses, efficiency, device current stress, cost, and total harmonic distortions are analyzed and evaluated respectively. Finally, advantages and disadvantages for each topology are discussed and highlighted. The evaluation and comparison methods presented in this paper and their results are feasible and effective for selecting the appropriate topology in practical applications under different operating conditions.

No abstract

Innovation is inseparable from the development of enterprise and the improvement of enterprises, and the improvement of innovation is inseparable from the supporting system. In the background of advocating supply-side reform in our country, this paper examines the adjustment of elements structure in the supply-side reform, by constructing models to analyze the need of money when enterprises decided to invest in innovation as well as how financial system affects their need. The result of the model shows that the interest rate of loan determinates whether the company decides to undertake technological innovation. Indirect financing market can stimulate enterprises' R&D through powering down the risk premium; direct financing market can promote R&D investment by adjusting the ratio between interest rate and riskless interest rate.