Investigation on smart bi-directional inverter with quantitative reactive power compensation and interleaved DC/DC converter for micro-grid system

Fan, Zaiming (2016) Investigation on smart bi-directional inverter with quantitative reactive power compensation and interleaved DC/DC converter for micro-grid system. Doctoral thesis, University of Cumbria (awarded by Lancaster University).

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Abstract

The PhD project aims to develop a smart grid-connected inverter (SGCI) for a micro-grid, which can be applied in a built environment such as a community, and associated power electronic DC/DC converters. The micro-grid generally includes distributed renewable power generators and battery storage. The SGCI is a bi-directional DC/AC inverter for distributed generation with battery storage installed at its DC side. In one aspect, it is expected the DC/AC inverter functions as a controlled inverter that can deliver expected real power to the power grid with quantitative reactive power compensation (RPC). In other words, all the SGCIs in the community microgrid can share the reactive power of the whole community because a SGCI can quantify its active and reactive power output. It is also expected that the inverter can work in both on-grid and off-grid modes. In other words, the DC/AC inverter functions as a controlled rectifier with high quality power factor correction (PFC), which can deliver expected DC power from the AC power grid at unity power factor. With the above features, battery storage on the DC bus of the SGCI can be charged/discharged through a four-phase, interleaved, bi-directional, boost/buck DC/DC converter (IBDBBC) for distributed renewable power system, either wind or solar PV or hybrid wind/solar PV system. The IBDBBC can discharge power from a low voltage battery to a high voltage DC bus as the IBDBBC operates in boost mode, or it can also draw power from the DC bus to charge the battery as the IBDBBC operates in buck mode. Based on MATLAB/Simulink, a mathematical model was developed for the grid-connected bi-directional DC/AC inverter that operates as a rectifier with PFC and as a grid-connected inverter (GCI) with expected real power output and quantitative RPC. In a practical application, the sampling of input signal through AD converter usually has some noise due to common-mode interference; simulation results demonstrate that the second order generalised integrator (SOGI) has great advantages to prevent interference. Therefore, SOGI can be utilised to construct a pair of orthogonal signals in a single-phase system to instantaneously split grid’s active and reactive power to achieve RPC for local community loads. The methodology of the constructed the pair of orthogonal signals was also used to generate the required reference current for the DC/AC inverter when which operated as a single-phase rectifier with PFC. Using three TI C2000 Solar Inverter DSK Boards, a small lab scale distributed power system was developed. In the lab distributed power system, the operating mode of the inverters could be switched between on-grid and off-grid through instruction from the control centre. The lab test outcomes demonstrate that each distributed power system unit worked properly under loss of power grid signal, simulating grid failure.

Item Type:	Thesis/Dissertation (Doctoral)
Departments:	Academic Departments > Science, Natural Resources & Outdoor Studies (SNROS) > STEM
Additional Information:	Thesis submitted for the degree of Doctor of Philosophy of the Lancaster University (University of Cumbria) Department of Engineering.
Depositing User:	Anna Lupton
Date Deposited:	17 Oct 2017 12:15
Last Modified:	12 Jan 2024 16:17
URI:	https://insight.cumbria.ac.uk/id/eprint/3326

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