Design and Implementation of a Low-Cost Phasor Measurement Unit: A Comprehensive Review

Abstract

The complexity of the contemporary electrical power systems imposes challenges in aspect of monitoring, protection and control. In order to obtain high speed of response, wide area effect and prices synchronization, the grid control functions can be benefited by the implementation of Phasor Measurement Units (PMU). The paper is aimed to make a review of the commercial implementation of Phasor Measurement Units and then open source based implementations (open architecture hardware and software). This paper focuses on standard implementations; as a consequence the concept of virtual PMU is not discussed here.

A Perturbation-Based Methodology to Estimate the Equivalent Inertia of an Area Monitored by PMUs

“…If the perturbation is a load step or disconnection, P re f should change to reflect that, but the problem is that in general, that perturbation is neither known nor measured directly. Here, such change in P re f is estimated as follows P re f (t) = P st1 L total , f or t < t e P re f (t) = P st2 L total , f or t ≥ t e (24) where P L total is the average value of the total load of the area at the steady-state before (st1) and after the perturbation (st2), and t e is the time of occurrence of the event. In this paper, P L total is assumed as known and t e is determined looking at power and voltage measurements.…”

“…However, monitoring generating units individually may be hard to ensure in real systems. Despite recent efforts on developing low-cost solutions [20][21][22], most commercial PMUs are still expensive [23,24], such that most countries still count with a limited number of PMUs installed. Hence, difficulties for TSOs are many: not all generators individually monitored, coherent groups always changing due to the impact of intermittent RES-based generation, lack of observability of medium-voltage and low-voltage grids, and limited or slow communication.…”

Error Model in Single-Board Computer-Based Phasor Measurement Units

“…It implements a synchronization mechanism of the time base with the time reference that is conceptually similar to a PLL, however without using any kind of close loop control. The time reference information generated by the GPS module is carried by the pulse-per-second (PPS) signal, mathematically defined by (7) as an infinite ideal pulse train with period…”

“…It implements a synchronization mechanism of the time base with the time reference that is conceptually similar to a PLL, however without using any kind of close loop control. The time reference information generated by the GPS module is carried by the pulse-per-second (PPS) signal, mathematically defined by (7) as an infinite ideal pulse train 𝛿 𝑝 with period 𝑇 𝛿 𝑝 (𝑡) = ∑ 𝛿(𝑡 − 𝑘𝑇) , ∞ 𝑘=−∞ (7) where 𝛿(𝑡) is the Dirac delta function. At the same time, the hardware PWM block inside the RPi microcontroller is responsible for generating the conversion time base…”

“…Despite their stated cost around 1000$ results much lower than traditional instruments, still it is too high for a realistic deployment in DN. Recent researches [7], however, are focusing on PMU architectures based on system on chip (SoC), embedded solutions which are proving to provide acceptable performance while further reducing the hardware cost by one order of magnitude. The SoC category can be further split in single board microcontroller and single board computer (SBC), consequently leading to different PMU design approaches.…”