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O'Donnell, Terence
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O'Donnell, Terence
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O'Donnell, Terence
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Now showing 1 - 10 of 17
- PublicationPlacement of Virtual Synchronous Generator Controlled Electric Storage combined with Renewable GenerationThe virtual synchronous generator (VSG) control of power converters has been proposed to improve the system inertia. The commonly used VSG requires an energy storage (ESS) to provide the emulated inertia power and the frequency droop power. The placement of the ESS can be either in the DC port of the power electronics generation or co-located with the power electronics generation on the AC side. In the former case, the VSG control makes the total generator behave like a synchronous generator, while in the latter one, the VSG control only regulates the ESS in response to the grid frequency. The different placement of the ESS gives rise to different performance. This paper analyzes this performance firstly by means of simple transfer function analysis and secondly by comparing their effects on the grid frequency at the system level in the IEEE 39 bus test system. The results show that the placement of the ESS has no impact on the system transient stability while it has a significant impact on the frequency dynamics especially in the low inertia situation.
305Scopus© Citations 9 - PublicationSmart transformer Modelling in Optimal Power Flow Analysis(IEEE, 2019-10-17)
; ; ; ; ; The smart transformer (ST) implemented using power electronics converters, has the capability of independent voltage control and reactive power isolation between its primary and secondary terminals. This capability provides a flexibility in the power system to support the voltage at the primary side and control the demand at the secondary side. Using this flexibility, the system power flow could, for example, be optimized for lower costs. This paper proposes an ST model suitable for OPF analysis. The effects of using multiple STs at different penetration levels, on the daily generation costs in an IEEE 39 bus test system are presented.331Scopus© Citations 3 - PublicationUse of voltage limits for current limitation in grid-forming converters(Power System Technology Press, 2020-02-13)
; ; Renewable generation interfaced through grid-forming converters are proposed as a replacement for synchronous generators in power systems. However, compared to the synchronous generator, the power electronics converter has a strict limit on the current to avoid overcurrent damage. The grid-forming converter acts like a voltage source, directily controlling the voltage. This conflicts with the operation of the conventional current limit control, which is applied to a current source. The switch between the voltage control and current control aimed to impose the current limit leads to synchronization instability. This paper proposes a novel control scheme which can be applied to the grid forming voltage control in order to enforce current limits. The proposed method has been verified through simulation and hardware tests in both symmetrical and asymmetrical faults to perform current suppression while maintaining synchronization stability in the voltage control mode.327Scopus© Citations 50 - PublicationMethodology for Assessment of the Impact of Smart Transformers on Power System ReliabilityThe smart transformer (ST) has been proposed as an alternative to the traditional low frequency transformer as a means to provide extra control functionality in the smart power system. The ST has merits in terms of reactive power decoupling and voltage decoupling at the primary and secondary side. This provides flexibility for reactive power compensation in the transmission system and demand reduction in the distribution system. Using its ability to control demand through voltage regulation, the ST provides the possibility to reduce demand while keeping the entire load online, which can provide an alternative to load curtailment. Thus, it may provide a means to improve power system reliability. However, no of previous research has investigated these potential system reliability benefits of the ST. The paper presents a methodology which can be used to quantify the system reliability impacts of the use of STs
442 - PublicationNeutral Current Optimization Control for Smart Transformer-fed Distribution System under Unbalanced Loads(IEEE, 2020-05-11)
; ; ; ; EU In a 3-phase 4-wire LV distribution system, unbalanced loads lead to neutral current (NC) looping resulting in increase of power losses and variation of neutral potential. Compared to the conventional power transformer, Smart Transformer (ST) has strict current limitations to avoid overcurrent. However, its advantages on the downstream LV grid voltage regulation can provides the capability to regulate excessive NC. This paper proposes a closed-loop NC optimization control in order to, on the one hand, minimize the NC current in the normal operation satisfying the standard EN 50160 requirement, on the other hand, suppress the NC current in extreme cases to avoid the overcurrent damage of the ST. The proposed control strategies are validated by experimental tests via the hardware-in-the-loop setup and a case study based on a 350kVA, 10kV/400V, ST-fed distribution network under unbalanced loading profile according to the 3-phase 4-wire distribution grid in Manchester area. The results clearly prove the effectiveness and flexibility of the proposed NC optimization control strategies on the NC suppression and minimization.362Scopus© Citations 14 - PublicationDesign of VSC Connected Low Frequency AC Offshore Transmission with Long HVAC CablesLow 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 - PublicationAnalysis of virtual synchronous generator control and its response based on transfer functionsVirtual Synchronous Generator (VSG) control has been proposed as a means to control power electronics converter interfaced generation and storage which retains the dynamics of the conventional synchronous machine. This study provides a comprehensive, transfer function based, analysis of VGS control, which can be used as the basis for the design of VSG transient and steady-state performance. Based on a hardware validated, large signal model, a small signal model and associated transfer functions which describe the changes in real and reactive powers in response to changes in references and grid frequency disturbances. The derived transfer functions are used to obtain insight into the correct design of VSG controllers. The small signal models, transfer functions and associated analysis are validated by comparison with measured results on a scaled hardware system.
470Scopus© Citations 34 - PublicationNeutral Current Minimization Control for Solid State Transformers under Unbalanced Loads in Distribution SystemsThis 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.
472Scopus© Citations 11 - PublicationModelling, Simulation and Hardware-in-the-Loop Validation of Virtual Synchronous Generator Control in Low Inertia Power System(IEEE, 2018-08-20)
; ; ; ; 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 - PublicationSmart Transformer for the Provision of Coordinated Voltage and Frequency Support in the Grid(IEEE, 2018-10-23)
; ; ; ; ; Considering the increase in renewable generation and the consequent reduction in power system inertia, the Virtual Synchronous Machine (VSM) control method has been proposed to control power converters to emulate the inertia and other the characteristics of the synchronous machine. However, to achieve the function of VSM control, an extra energy base, typically storage, is required to connect to the controlled converter. In this work we investigate the application of the VSM control to the distribution system demand through the use of a VSM controlled smart transformer. Through control of the demand in this way, the demand itself can be used to emulate inertia and provide frequency support. This paper presents the details of the flexible demand control applied to a smart transformer supplying a low voltage distribution grid. The operation of the control is validated on scaled hardware using real time simulation with hardware in the loop. Simulations on a 400 kVA, 400 V distribution network are used to quantify the demand flexible. IEEE 39 bus is used to verify the benefit of the proposed control in terms of voltage and frequency in the power system.433Scopus© Citations 15