O'Loughlin, Cathal

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O'Loughlin, Cathal
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O'Loughlin, Cathal

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  • Publication
    Neutral Current Minimization Control for Solid State Transformers under Unbalanced Loads in Distribution Systems
    (IEEE, 2018-12-03)
    Chen, Junru 
    ;
    Yang, Tao 
    ;
    O'Loughlin, Cathal 
    ;
    O'Donnell, Terence 
    This paper analyses the neutral current reduction performance of a three phase four leg solid state transformer (SST) under different degrees of unbalanced load. Several kinds of control strategies are presented, the neutral current elimination controls which rely on phase shifting, voltage amplitude and phase shifting & voltage amplitude combination control. A neutral current minimization control which ensures the SST output voltages complies with the EN 50160 output voltage unbalance standard is also developed. These control approaches simply build on the balanced voltage control providing voltage references which slightly unbalanced the voltage amplitude and phase angle or both. The effectiveness of the proposed strategies is validated through tests on a downscaled prototype. Simulation results for the neutral current minimization control of the SST applied to a real urban distribution network with distributed loads are presented. The results of this analysis show that overall the neutral current minimization results in an energy saving from both reduced losses in the distribution cables and reduced power consumption in the load.
      473Scopus© Citations 11
  • Publication
    Modelling, Simulation and Hardware-in-the-Loop Validation of Virtual Synchronous Generator Control in Low Inertia Power System
    (IEEE, 2018-08-20)
    Chen, Junru 
    ;
    Liu, Muyang 
    ;
    O'Loughlin, Cathal 
    ;
    Milano, Federico 
    ;
    O'Donnell, Terence 
    In recent literature, virtual synchronous generator control (VSG) has been proposed as a means to provide virtual inertia from non-synchronous generation in low inertia power systems. In this work we compare the power system support performance of VSG control to conventional droop when applied to electrical energy storage. A differential-algebraic equations (DAEs) model of VSG control is developed. This model is validated against measurement from a hardware in the loop implementation of the VSG. VSG and droop controlled storage is then incorporated into the IEEE 39 bus system model also incorporating different levels of generation from windfarms. The performance of both controls is compared in terms of their effect on the power system dynamics in the event of a contingency. The results show that VSG control in high wind penetration cases, improves the frequency nadir, reduces oscillations, and provide faster frequency and voltage stabilization.
      785Scopus© Citations 21
  • Publication
    Design of VSC Connected Low Frequency AC Offshore Transmission with Long HVAC Cables
    (IEEE, 2017-12-07)
    Ruddy, Jonathan 
    ;
    Meere, Ronan 
    ;
    O'Loughlin, Cathal 
    ;
    O'Donnell, Terence 
    Low frequency ac transmission (LFAC) has been proposed as an alternative to high voltage dc transmission for medium distance (80-150 km) offshore wind farms. Long HVAC cables and their associated low frequency resonance, connected to voltage source converters (VSC), provide technical challenges for the control of the offshore voltage. This paper provides the design of the offshore voltage 'grid forming control' to maintain a stable offshore voltage accounting for the connection of a long HVAC cable connected to the VSC. Simulations are performed on an LFAC test system to examine the influence of controller parameters and the associated design tradeoffs between the selection of dq controller time constants and voltage control bandwidth. The LFAC system design and control is then validated in a hardware experiment where the proposed controller operates in a real-Time hardware-in-The-loop experiment.
      502Scopus© Citations 26
  • Publication
    Harmonic stability of VSC connected Low Frequency AC offshore transmission with long HVAC cables
    (Elsevier, 2018-09)
    Ruddy, Jonathan 
    ;
    Chen, Junru 
    ;
    Meere, Ronan 
    ;
    O'Loughlin, Cathal 
    ;
    O'Donnell, Terence 
    Low Frequency AC (LFAC) transmission has been proposed as an alternative to HVDC transmission for the integration of offshore wind. The LFAC offshore grid as a fully power electronic grid with a long HVAC cable provides significant challenges to harmonic stability. This paper presents an impedance based stability analysis to determine the stability of the power electronic offshore system across the harmonic frequency range. The stability analysis is introduced and applied to the LFAC system. The impact of different current and voltage control bandwidths and component sizes on the dynamic impedance of the converters is then examined and their impact on harmonic stability of the LFAC grid is determined. It is found that detailed knowledge of the control parameters and the ability to tune the bandwidths can mitigate significant harmonic instability with the presence of a long HVAC cable. Three phase simulations are then used to validated the impedance based stability technique.
      496Scopus© Citations 7