The ever-increasing integration of renewable energy sources within modern power systems has significant benefits from the economic and environmental point of view, but poses also some technological challenges that shall be addressed to guarantee a safe and continuous service. Distributed energy resources are connected via dedicated inverters, whose power electronic circuitry does not provide any rotational inertia and switches at high frequency introducing harmonic and inter-harmonic pollution into the network. Consequently, the traditional sinusoidal model for the power signal is not valid anymore and new measurement procedures and instruments shall be developed. In this sense, the main requirements are the accurate tracking of the fundamental frequency and ROCOF during system dynamics and the capability to reject spurious interferences in the range from DC to few kHz.For these reasons, a new generation of PMUs is envisioned. The reference IEC / IEEE Std 60255-118-1:2018 defines the PMU performance requirements in terms of estimation accuracy and reporting latency, making specific reference to a transmission network scenario. The scientific literature as well as the instrument market propose a wide variety of solutions that are compliant with the IEC /IEEE Std. However, a series of system contingencies recently occurred in South Australia and European interconnected network are proofs of the need for more sophisticated instruments, capable of detecting and correctly identifying transients that were not included in the standard. Based on these considerations, the proposed project builds up on the results of ACSICON and SCCER-FURIES projects [10] that focused on the stability impact of the transmission system after the massive integration of converter interface generation (CIG) and aims at developing, characterizing and validating a new PMU prototype specifically designed to equip the system operators with more reliable measurements, particularly for low-inertia power systems.The new PMU prototype shall be characterized by high-accuracy in dynamic conditions (e.g. frequency errors in the order of 100 mHz during sinusoidal or quadratic phase modulations) as well as reduced latency (i.e. in the order of few tens ms). The PMU frequency measurements will allow for a more precise and prompter identification of network inertia modifications and thus allow for a more effective counteraction. One of the objectives of the project is to characterize the prototype not only in standard test conditions, but in realistic operating conditions, by means of hardware-in-the-loop simulations. Indeed, a crucial point for the development of this technology is the assessment of its reliability when deployed on-the-field. A clear understanding of which phenomena can be properly captured, and which produce inaccurate estimates, will allow for defining the confidence interval of the PMU estimates in the different applications (inertia monitoring, protection, etc).In conclusion, the expected outcome of the project is the development and full characterization of a new PMU prototype that not only meets the standard requirements but is also designed to cope with the challenges of low-inertia networks.