The burn-in test of three-phase UPS by energy feedback method
In the burn-in test of three-phase online uninterruptible power supply (UPS) system, RLC is usually used as a load in the conventional method. For saving energy and decreasing the test cost of UPS, the energy feedback method is proposed to apply the test of the online UPS. In this method, the utility system is used instead of a load. A voltage regulator is used in parallel operation to turn back the energy, which was dissipated in conventional method, to the utility system. The values of real power and reactive power in the output of UPS can be regulated in the proposed method to imitate various loads. From the experimental results, the efficiency of saving energy is more than 85% near half-load and will be higher while the load increases.<<ETX>>
Aalborg Universitet Multi-Mode Operation for On-line Uninterruptible Power Supply System
To enhance the robustness and disturbance rejection ability of an on-line uninterruptible power supply (UPS) system, an Internal Model Control (IMC)-based DC-link voltage regulation method is proposed in this paper. Furthermore, the multi-mode operations of the on-line UPS system are investigated and their corresponding control strategies are proposed. The proposed control strategies are capable of achieving the seamless transition in traditional normal mode, PV-aided normal mode, enhanced eco-mode and burn-in test mode. Meanwhile, the uninterruptible load voltage is promised during the mode transition. The small signal analysis is also conducted to investigate the stability of enhanced eco-mode and burn-in test mode. Finally, extensive experimental results are provided to validate the effectiveness of the proposed methods.
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.