Analysis and modeling of novel brushless exciter based on hybrid excitation topology
The exciter is a key component of the synchronous generator system with self-excited initiation. Based on the topology of hybrid excitation, this paper proposes a novel brushless exciter, which is suitable for an isolated power system. The parameters of the exciter are calculated by the numerical method based on finite element model, and the state space model is established. The experimental researches are carried out on a 3 kW prototype.
Research on self-excited initiation of a Medium-voltage DC (MVDC) multiphase synchronous generator-rectifier system
This paper has described the excitation system of a Medium-voltage DC (MVDC) multiphase synchronous generator-rectifier system and calculated the minimum frequency of the pilot-exciter needed for self-excited initiation. On this basis, a double closed-loop V/F control method is proposed according to the classical PI control algorithm for self-excited initiation. With the method, a prototype is constructed for test. The results show that both the self-excitation initiating and the speed-rising processes of the generator set have changed synchronously thus to reduce the time needed for MVDC multiphase synchronous generator-rectifier system to start and finish establishing the nominal DC voltage.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.