Investigation on smart bi-directional inverter with quantitative reactive
      power compensation and interleaved DC/DC converter for micro-grid system
Creators: name: Fan, Zaiming
Publisher: name: Lancaster University
Year: 2016

description: 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.