Antonino Riccobono

Stability and accuracy analysis of power hardware in the loop system with different interface algorithms

The power hardware in the loop (PHIL) technology allows for testing a physical device under test (DUT) connected to the real time simulated rest of system (ROS) through a power electronic interface and interface algorithm (IA). Stability and accuracy questions remain open due to the non-ideal interface converter. This paper presents a frequency-domain stability analysis and a time-domain accuracy analysis of the PHIL system with different IAs, taking into account of the delay factors in the PHIL system. Results show that the damping impedance method (DIM) IA can realize a perfectly stable PHIL system, while the ideal transformer model (ITM) IA needs be modified to stabilize the PHIL system. The voltage and current expressions at both ROS side and DUT side are derived to make considerations about the accuracy of the PHIL system. Results show that matching of the waveforms at ROS and DUT sides can be achieved for passive DUTs with the DIM IA; however, for active DUTs, the matching suffers from the delay factors.

Wideband identification of impedance to improve accuracy and stability of power-hardware-in-the-loop simulations

The Power Hardware in the Loop (PHiL) technique, critical for power systems where testing grid connected power converters may be difficult, allows connecting a real Device Under Test (DUT) with the real-time simulated Rest Of System (ROS) at power level. An Algorithm Interface (IA) and a power amplifier connect ROS and DUT. This paper presents the application of the Wideband System Identification (WSI) technique, an online method to measure impedance over a wide frequency range, combined with the Damping Impedance Method (DIM) IA, to improve both accuracy and stability of a PHiL test bench. First, the impedance of the DUT is identified via the WSI. Then, the DIM IA is updated with the measured wide frequency range impedance of the DUT. The application of the method is illustrated for the scenario of a PHiL test of a DC microgrid with a passive load.

Online wideband identification of single-phase AC power grid impedances using an existing grid-tied power electronic inverter

This paper presents an original implementation, in an embedded controller, of a recently proposed online wideband single-phase AC system impedance identification technique and its validation via a Hardware In the Loop (HIL) real-time simulation setup. The technique uses an existing grid-tied inverter for estimation of wide bandwidth single-phase AC grid impedance in addition to performing its original power conversion function. A small-signal Pseudo Random Binary Sequence (PRBS), a digital approximation of white noise, can be super-imposed on the inverter switching commands. This injected white noise signal is wide bandwidth in nature, and, using appropriate cross correlation techniques, the wideband AC grid impedance can be measured. In smart grid applications, online wideband monitoring of AC power grid impedances is a key enabler of a set of capabilities, such as health monitoring, active filter retuning, and adaptive control of inverters. To evaluate the effectiveness of the online wide bandwidth AC power impedance identification technique in all of these smart grid applications, the proposed HIL setup aims at the numerical evaluation of the identification technique performance as well as the evaluation of all practical implementation issues.

Next generation automation architecture for DC smart homes

DC nanogrids for residential use are gaining research interest as an effective solution to integrate several types of distributed renewable energy resources, energy storage, and DC loads. This paper proposes a novel three-layer automation architecture for the DC nanogrid of future DC “smart” homes. The bottom layer, i.e. the converter level control, is fully decentralized and allows plug&play functionality, without the need for horizontal communication. The middle layer optimizes the usage of energy resources and storage as well as thermal (heating/cooling) devices based on a Multi-Agent System. The top layer is the user interface and the communication port to the Energy Network Operator, to enable smart grid capabilities, such as demand side management, demand response, and grid support. This paper presents the draft architecture together with a preliminary analysis of standard protocols for building automation which can be used to identify the best solutions for the communication that supports the architecture.

Online wideband identification of three-phase AC power grid impedances using an existing grid-tied power electronic inverter

In smart grid applications, online wideband monitoring of AC power grid impedances is a key enabler of a set of capabilities, such as active filter tuning, adaptive control of inverters, and monitoring of local grid status, from which stability margins can be calculated. To evaluate the effectiveness of online wideband monitoring of AC power grid impedances in smart grid applications, this paper presents the implementation, in an embedded controller, of a recently proposed online Wideband System Identification (WSI) technique, validated via Hardware In the Loop (HIL) real-time simulation. The identification technique exploits an existing grid-tied inverter for the estimation of wide bandwidth AC grid impedances, on top of the original power conversion function. This is accomplished by super-imposing a small-signal Pseudo Random Binary Sequence (PRBS), a digital approximation of white noise which is wide bandwidth in nature, on the inverter switching commands so that all frequencies of interest can be excited at once. Then, after postprocessing, the wideband AC grid impedance can be extracted using appropriate cross correlation techniques. The present work focuses on the identification of balanced three-phase AC power grid impedances in the three-phase reference frame.

Systematic method for the development of future active distribution network automation architectures

In response to the EU Mandate M/490, two crucial tools were developed for supporting the standardization of the Smart Grid: the Smart Architecture Model (SGAM) framework and the Use Case Methodology. This paper shows and exemplifies the use of these tools to incrementally develop the automation architecture for future active distribution power systems, by leveraging on existing automation architectures from literature and existing standards. This method for architecture development has been formalized and used in EU Project IDE4L, but it is generally applicable.

Noninvasive Online Parametric Identification of Three-Phase AC Power Impedances to Assess the Stability of Grid-Tied Power Electronic Inverters in LV Networks

This paper presents a noninvasive online parametric identification of three-phase ac power impedances to assess small-signal stability of grid-tied inverter systems by using well-known impedance-ratio-based stability criteria. The identification technique is integrated into the control of an existing grid-tied inverter for the estimation of wide bandwidth ac grid impedances, on top of its original power conversion function. This is accomplished in practice by injecting a short-time small-signal pseudorandom binary sequence (PRBS), a digital approximation of white noise which is wide bandwidth in nature, on the inverter control loop so that all frequencies of interest at the impedance measurement point can be excited at once. Then, digital processing is performed in the integrated control platform where the parametric ac grid impedance is extracted from the measurement of voltage and current over the length of PRBS injection. Moreover, a procedure on how to identify the output impedance of the inverter is deployed so that the parametric source and load impedances can be used to verify the system stability by means of the generalized Nyquist stability criterion. The technique is validated via hardware-in-the-loop real-time simulation. This paper focuses on the identification of balanced three-phase ac impedances in dq reference frame and a dq diagonal-dominant stability analysis which is typical of low-voltage distribution grids.

Online Parametric Identification of Power Impedances to Improve Stability and Accuracy of Power Hardware-in-the-Loop Simulations

This paper presents the wideband system identification (WSI) technique, i.e., an online method to identify power impedances over a wide frequency range from which the corresponding parametric impedance can be calculated online as well. The WSI technique exploits an existing custom 25-kW power electronic converter on the top of its power conversion function, which serves as power amplifier of an existing power hardware-in-the-loop (PHiL) simulation setup. The PHiL simulation technique allows connecting a real device under test (DUT) with the real-time simulated rest of system (ROS) at power level. An interface algorithm (IA) on simulation side and a power amplifier (the 25-kW power electronic converter) connect ROS and DUT. This paper shows the impact of the uncertainties in the WSI chain on the accuracy of the impedance identification and highlights how the WSI technique can be combined with the damping impedance method IA to improve both accuracy and stability of the PHiL test bench. The application of the method is illustrated for the scenario of a PHiL test of a dc microgrid with a passive load.

Stability of Shipboard DC Power Distribution: Online Impedance-Based Systems Methods

Many modern commercial ships are electric ships, i.e., they utilize integrated electric propulsion (IEP ), where electric motors with variable speed drives are used for ship propulsion. This provides a number of advantages, such as reduced size and weight, electric power availability aboard the ship, reduced vibration, and more flexibility in generation engine placement by eliminating the mechanical connection between engines and propulsion. Most cruise ships, many yachts, and even cargo ships utilize IEP. There is also significant interest in IEP for military ships.