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Insulation monitoring is crucial to personal safety and equipment operation in the power distribution system. Recently, with the rapid development of distributed generators, the three-phase voltage-source PWM converter (VSC) is widely used as the bidirectional interface between the dc microgrids and the distribution networks. This paper presents the relationship between the response of insulation monitoring device (IMD) and the neutral-point voltage deviation (NPVD) of VSC, by analyzing the disturbances of the switching function and the dc-side insulation balancing. Then, a method of detecting the NPVD for grid-connected VSC is proposed, based on the dc signal injection and the Duffing oscillator. Furthermore, the proposed method takes the mean and spectrum of the neutral-point voltage as the primal characteristics. Thus, the dc signal injection is adopted to detect the mean of the neutral-point voltage, and the Duffing oscillator is adopted to determine the frequency disturbance of the neutral-point voltage, respectively. The test result confirms the existence of the neutral-point voltage deviation and verifies the availability of the proposed method. Hence, the proposed method could be used to improve the response of IMD. [ABSTRACT FROM AUTHOR]

The uptake of variable megawatts from photovoltaics (PV) challenges distribution system operation. The primary problem is significant voltage rise in the feeder that forces existing voltage control devices such as on-load tap-changers and line voltage regulators to operate continuously. The consequence is the deterioration of the operating life of the voltage control mechanism. Also, conventional non-coordinated reactive power control can result in the operation of the line regulator at its control limit (runaway condition). This paper proposes an optimal reactive power coordination strategy based on the load and irradiance forecast. The objective is to minimize the number of tap operations so as not to reduce the operating life of the tap control mechanism and avoid runaway. The proposed objective is achieved by coordinating various reactive power control options in the distribution network while satisfying constraints such as maximum power point tracking of PV and voltage limits of the feeder. The option of voltage support from PV plant is also considered. The problem is formulated as constrained optimization and solved through the interior point technique. The effectiveness of the approach is demonstrated in a realistic distribution network model. [ABSTRACT FROM PUBLISHER]

In telecom applications, the vision for a total power conversion efficiency from the mains to the output of point-of-load (PoL) converters of 95% demands optimization of every conversion step, i.e., the power factor correction (PFC) rectifier front-end should show an outstanding efficiency in the range of 99%. For recently discussed 400-V dc distribution bus voltages, a buck-type PFC rectifier is a logical solution. In this paper, an efficiency-optimized, 98.8% efficient, 5-kW three-phase buck-type PFC rectifier with 400-V output is presented. Methods for calculating losses of all components are described and are used to optimize the converter design for efficiency at full load. Special attention is paid to semiconductor losses, which are shown to be dominant, with the parasitic device capacitance losses being a significant component. The calculation of these parasitic capacitance losses is treated in detail, and the charge-balance approach used is verified. A prototype of the proposed rectifier is constructed which verifies the accuracy of the models used for loss calculation and optimization. [ABSTRACT FROM AUTHOR]