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Conventionally, standard proportional and integral (PI) controllers with constant PI gains are commonly used for the dc-link voltage control of single-phase grid-connected converters (GCCs). For such controllers, the selection of the PI gains will lead to a tradeoff between two control objectives: 1) the reduction of the dc-link voltage fluctuations caused by random swings of the active power drawn by the single-phase GCC; and 2) the reduction of the grid current harmonics mainly caused by the 2f oscillation of the active power in single-phase applications. To solve this tradeoff, this paper presents a systematic approach for the design of an adaptive PI controller for the dc-link voltage control of single-phase GCCs. The proposed design approach is simple and it provides a convenient method to properly determine the adaptive PI controller parameters. Representative simulation and experimental results are presented and discussed in order to show the effectiveness of the proposed dc-link voltage controller. [ABSTRACT FROM AUTHOR]

Grid-connected converters (GcCs) employ LCL filters instead of simple L filters in order to meet new grid codes and their on-going changes in the near future. Active damping methods, without power losses, are preferred to passive ones for solving the resonance problems of LCL-filter-based GcCs ( LCL-GcCs). However, large changes in the grid inductance (typically under weak grid conditions and in rural areas) may compromise the system stability. Moreover, the delay of digital controllers will change system phase-frequency characteristics and consequently will affect the system stability. In view of this, this paper proposes a systematic design procedure for the active damping of voltage-oriented PI control for LCL- GcCs. The procedure considers active damping methods based on capacitor current feedback and is aimed to ensure stable operation under severe grid inductance variations while taking into account the influence of digital control delay and LCL filter parameters changes on the system stability. Simulation and experimental results are presented and discussed in order to validate the proposed design procedure. [ABSTRACT FROM PUBLISHER]

This paper presents a grid-connection control strategy of doubly fed induction generator wind system based on the direct control of both a virtual torque and rotor flux of the generator. This control is achieved with no proportional-integral regulator and requires the measurement of only grid voltages, Eotor currents, and rotor position. The same switching table is used for grid synchronization and for running process. A field-programmable-gate-array-based design of the proposed control is developed and tested on a 4-kW experimental prototype. Experimental results are provided to show the effectiveness of the fast and soft grid-connection method developed. [ABSTRACT FROM AUTHOR]

Highlights • A state of art of DC bus voltage for residential DC microgrid is addressed. • A survey of DC home appliances available on the market is performed as well as electrical safety in LVDC is addressed. • A performance comparison of some DC bus voltage level chosen for a small house case study is performed, followed by a financial analysis. Abstract This paper outlines a survey of DC bus voltage levels for standalone residential DC nanogrid. The DC bus, located between distributed generators and loads in DC nanogrid application, is generally chosen from existing experience and practices. A disparity of voltage levels is found in the literature due to lack of standardization, although some organizations actually deal with developing these standards. From this standpoint, this work proposes to present the elements to be taken into account in order to reach an adequate voltage level choice for a given application. User safety, efficiency and cost saving have to be ensured by this choice. Therefore, criteria based on power consumption, area of application deployment, cable size, line transmission losses are considered. The approach is applied to a small scale laboratory system with low power consumption and led to the choice of 48 V DC bus. [ABSTRACT FROM AUTHOR]