Nowadays, traditional synchronous generators are replaced by distributed renewable energy sources (DRESs), which are connected to the grid via power converters. This shift towards non-synchronous generation leads to low inertia power systems and affects considerably the frequency control procedure. To provide an inertial response and to enhance grid stability, DRESs can be equipped with fast discharging energy storage systems, such as ultracapacitors. This feature allows distribution system operators (DSOs) to provide an inertial response as ancillary service to transmission system operators (TSOs) by coordinating the operation of many DRESs. For this purpose, DSOs should develop tools to quantify and control the provision of inertial response. Towards this objective, in this study, two new methodologies are proposed. The first one aims to evaluate the maximum aggregated inertial capability of active distribution networks (ADNs). The second one aims to dispatch DRESs to provide specific, TSO-defined, inertial response with the minimum cost. Both methods are tested on a medium voltage grid. Several cases are examined highlighting the impact of different parameters, such as converter limitations, line congestions, on the inertial capability of ADNs. Results indicate that the proposed methods can fully exploit operational limits of ADNs and maximise their inertial capability.

The ability to detect single photons is becoming an enabling key capability in an increasing number of fields. Indeed, its scope is not limited to applications that specifically rely on single photons, such as quantum imaging, but extends to applications where a low signal is overwhelmed by background light, such as laser ranging, or in which faint excitation light is required not to damage the sample or harm the patient. In the last decades, SPADs gained popularity with respect to other single-photon detectors thanks to their small size, possibility to be integrated in complementary metal-oxide semiconductor processes, room temperature operability, low power supply and, above all, the possibility to be fast gated (to time filter the incoming signal) and to precisely timestamp the detected photons. The development of large digital arrays that integrates the detectors and circuits has allowed the implementation of complex functionality on-chip, tailoring the detectors to suit the need of specific applications. This review proposes a complete overview of silicon SPADs characteristics and applications. In the previous Part I, starting with the working principle, simulation models and required frontend, the paper moves to the most common parameters adopted in literature for characterizing SPAD performance and describes single pixels applications and their performance. In this Part II, the focus is posed on the development of SPAD arrays, presenting some of the most notable examples found in literature. The actual exploitation of these designs in real applications (e.g., automotive, bioimaging and radiation detectors) is then discussed.

We present an array of 16 × 16 single-photon avalanche diodes (SPADs) with 16 shared 6 ps time-to-digital converters (TDCs), designed for non-line-of-sight imaging. It features a timing jitter of 60 ps (FWHM), fast-gated capabilities and up to 1.6•10 8 photon time-tagging measurements per second.

The ability to detect single photons is becoming an enabling key capability in an increasing number of fields. Indeed, its scope is not limited to applications that specifically rely on single photons, such as quantum imaging, but extends to applications where a low signal is overwhelmed by background light, such as laser ranging, or in which faint excitation light is required not to damage the sample or harm the patient. In the last decades, SPADs gained popularity with respect to other single-photon detectors thanks to their small size, possibility to be integrated in Complementary Metal-Oxide Semiconductor processes, room temperature operability, low power supply and, above all, the possibility to be fast gated (to time filter the incoming signal) and to precisely timestamp the detected photons. The development of large digital arrays that integrates the detectors and circuits has allowed the implementation of complex functionality on-chip, tailoring the detectors to suit the need of specific applications. This review proposes a complete overview of silicon SPADs characteristics and applications. In this Part I, starting with the working principle, simulation models and required frontend, the paper moves to the most common parameters adopted in literature for characterizing SPADs, and describes single pixels applications and their performance. In the next Part II, the focus is then posed on the development of SPAD arrays, presenting some of the most notable examples found in literature. The actual exploitation of these designs in real applications (e.g., automotive, bioimaging and radiation detectors) is then discussed.

We present the design and characterization of a fully-integrated array of 16 × 16 Single-Photon Avalanche Diodes (SPADs) with fast-gating capabilities and 16 on-chip 6 ps time-to-digital converters, which has been embedded in a compact imaging module. Such sensor has been developed for Non-Line-Of-Sight imaging applications, which require: i) a narrow instrument response function, for a centimeter-accurate single-shot precision; ii) fast-gated SPADs, for time-filtering of directly reflected photons; iii) high photon detection probability, for acquiring faint signals undergoing multiple scattering events.Thanks to a novel multiple differential SPAD-SPAD sensing approach, SPAD detectors can be swiftly activated in less than 500 ps and the full-width at half maximum of the instrument response function is always less than 75 ps (60 ps on average). Temporal responses are consistently uniform throughout the gate window, showing just few picoseconds of time dispersion when 30 ns gate pulses are applied, while the differential non-linearity is as low as 250 fs. With a photon detection probability peak of 70% at 490 nm, a fill-factor of 9.6% and up to 1.6 • 10 8 photon time-tagging measurements per second, such sensor fulfills the demand for fully-integrated imaging solutions optimized for non-line-of-sight imaging applications, enabling to cut exposure times while also optimizing size, weight, power and cost, thus paving the way for further scaled architectures.