Manuscript submitted to the IEEE Industry Applications Society’s Open Journal of Industry Applications on September 2023. Abstract: Power hardware-in-the-loop (PHIL) is a modern experimental technique that allows emulation of a full-scale converter (FSC) with the combination of a scaled-down converter (SDC), power amplifier, and real-time simulator, thus enabling the study of real-time interactions of power electronics with large power systems. However, assembling an accurate scaled-down replica of an FSC with off-the-shelf laboratory SDCs is practically impossible due to a mismatch in per unit losses, as well as in the impedance of the L/LC/LCL filter. Consequently, the scaled-up power flow capability of SDCs differs from FSCs, restricting emulation to smaller regions of the four quadrants than those corresponding to the FSCs nominal active and reactive capacity. These PHIL test beds cannot be used to emulate FSCs demanding bidirectional active and reactive power flow. Any scaling method on SDCs, emulating the entire operation of FSCs, demands underutilisation of SDCs, reducing the advantages of PHIL tests. This paper, therefore, proposes a physics-informed scaling method that exploits power capability curves to emulate FSCs in all four quadrants of operation. This method is independent of SDC topology, filter type, and interfacing methods. A visual identification of the semiconductor device constraints bounding the emulation is also presented, utilizing the physics of converter control. A theoretical analysis of the proposed method is presented, followed by validation with MATLAB simulations and experimental tests using a 50 kVA SDC.

Manuscript submitted to the IEEE Industry Applications Society’s Open Journal of Industry Applications on January 2023. Abstract: Power hardware-in-the-loop (PHIL) is an experimental technique that uses power amplifiers and real-time simulators for studying the dynamics of power electronic converters and electrical grids. PHIL tests provide the means for functional validation of advanced control algorithms without the burden of building high-power prototypes during early technology readiness levels. However, replicating the behavior of high-power systems with laboratory scaled-down converters (SDCs) can be complex. Inaccurate scaling of the SDCs coupled with an exclusive focus on instantaneous voltages and currents at the fundamental frequency can lead to PHIL results that are only partially relatable to the high-power systems under study. Test beds that fail to represent switching frequency harmonics cannot be used for studying harmonic penetration or loss characterization of large-scale converters. To tackle this issue, this paper proposes a harmonic-invariant scaling method (HISM) that exploits the VA rating of preexisting laboratory SDCs for more accurately replicating harmonic phenomena in a PHIL test bench. Firstly, a theoretical analysis of the proposed method is presented and, subsequently, the method is validated with MATLAB simulations and experimental tests.

Manuscript submitted to the IEEE Transations in Power Systems in October 2022. Title: Coordination of Frequency Reserves in an Isolated Industrial Grid Equipped with Energy Storage and Dominated by Constant Power Loads Abstract: This paper examines the use of interconnected synchronous system requirements for frequency containment reserves (FCR) on isolated industrial grids that use turbogenerators as main source of energy, have high penetration of wind energy, are equipped with energy storage, and have a high level of constant power loads coupled by power electronic converters. Leveraging on the recent Nordic requirements for reserves in islanded operation (FCRI), we propose an expansion that allows prioritizing among various reserve providers under different isolated grid conditions. The study case of a complex, isolated industrial grid is selected to test this approach. The stability of this grid is evaluated via eigenvalues and participation factors considering the detrimental effects of constant power loads. It is demonstrated that, by prioritizing the reserve allocation to the faster converter-interfaced storage devices and loads, the overall stability is increased in addition to allowing the turbogenerators to operate at a more constant load. The results are supported by computer simulations of a rotating mass model, of the complex isolated grid in PowerFactory, and by laboratory power-hardware-in-the-loop tests. The computer simulation models developed for this paper are made publicly available for reproducibility purposes.

Manuscript submitted to the Twenty-second IEEE Workshop on Control and Modeling for Power Electronics (COMPEL 2021). Abstract: Dual-sequence current controllers of voltage source converters (VSCs) feature two separate rotating reference frames (RRFs), commonly named dq frames, and rely on techniques that isolate the positive and negative sequences of three-phase measurements. One of these techniques is the delayed signal cancellation (DSC). It is performed in the stationary reference frame (SRF), also known as αβ frame. The DSC combines old values of one axis with new values of the other axis of the SRF. The results are, then, transformed into the RRFs for use in the current controller. This filtering process introduces an extra layer of complexity for dual-sequence current controllers, which could otherwise operate solely in the RRFs. This paper introduces a frequency adaptive DSC method that operates directly in the RRF. Moreover, an averaging of two of the proposed DSC filters with contiguous integer delays is employed for reducing discretization errors caused by grid frequency excursions. A formal proof of the equivalence between the αβ and dq DSC methods is presented. Furthermore, computer simulations of a case study support the interpretation of the results.

This paper was accepted for presentation at the IEEE CPE-POWERENG 2021 conference held in Florence, Italy, between the 14th and 16th of July 2021. It investigates the root causes of detrimental oscillations in the dc link voltage of an energy storage system using a dual dq controller, operating at a high-voltage ac grid with high reactance-resistance ratio. Dual dq controllers are recommended in the literature for power converters operating under unbalanced, fault, or reduced voltage conditions. They employ two separated rotating reference frames, one for the positive and one for the negative sequence. The causes of the oscillations are investigated both theoretically and by time-domain computer simulations. As a result of the simulations, the performance of two dual controllers used in the industry is compared. In the presence of exponentially decaying dc currents, the filtering techniques employed by the controllers affect differently the performance of the proportional-integral regulators and disturb the feed forwarding and dq decoupling schemes. Ultimately, this results in undesirable oscillations in the dc-link voltage. This paper sheds light on how a fundamental phenomenon of three-phase ac systems can critically affect the control of power electronic converters. It provides a valuable insight into a possible root cause of oscillations in large electrical system applications with a considerable power converter penetration, such as large industrial plants striving for reducing greenhouse gas emissions.