Operation and Control in Smart Electric Power Systems: Methods and Applications

The distributed power generation is increasing rapidly, and its integration into the power system is a critical issue for the existing power network. Therefore, a three-level converter is developed to access and control the medium voltage DC generated from a photovoltaic system in a smart grid. A conventional three-level neutral point clamped circuit is incorporated into the conventional inverter. The conventional inverter is a pulse width modulation-based inverter that achieves zero switching currents and supplies power to the load. This technique suppresses the switching power loss up to a large extent. Additionally, switches conduct half of the input voltage; therefore, the output voltage is significantly similar to the voltage of the output filter. Moreover, in the proposed converter, the stress of voltage on diodes is minimal, which increases the input range of voltage in smart grids. The overall efficiency of converter is around 97.9% and voltage gain is around 42. In addition to these, a detailed design description and analysis are carried out in this paper. In the end, a prototype is developed for experimental analysis to validate the operating principle and characteristics of the proposed converter.

Compared to conventional DC transmission, Voltage source converter based high voltage direct current transmission (VSC-HVDC) has the advantages of independently controllable transmission power, no commutation failure, no reactive power compensation and low harmonic levels. However, VSC-HVDC transmission cannot provide effective frequency support and regulation for the system after grid connection. For this reason, an adaptive neural fuzzy virtual inertia control method is proposed to impose a control strategy on the converter at the receiving end of a VSC-HVDC transmission. The method uses the frequency change rate and the amount of change of frequency as constraints to dynamically adjust the virtual inertia and damping coefficients. It provides larger inertial support when the frequency fluctuation is large and smaller inertial support when the frequency fluctuation is small, thus adapting to different operating conditions. Finally, a hardware-in-the-loop simulation platform is built. The superiority and application prospect of the proposed strategy in frequency stability of the system are verified by comparing the proposed strategy with the traditional virtual control strategy.