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OPQBox2

Second generation open power quality measurement device

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Overview

The mission of the Open Power Quality project is to design and implement open source hardware, software, and data for low cost, crowd-sourced power quality monitoring, storage, and analysis. For more details, please see our home page.

This repository provides the proposed schematics for the second generation Open Power Quality metering device (OPQBox2).

OPQBox2 is in the final design stage. We are circulating this design to solicit feedback and make improvements prior to production. We greatly appreciate your willingness to provide us with feedback.

Goal

The goal of OPQBox is to monitor voltage and frequency and detect departures from nominal levels. It accomplishes this by sampling the waveform 256 times per cycle, extracting power quality measures (including frequency, RMS voltage, and THD), and then uploading data about these measures to the OPQHub service.

OPQBox can be configured to send a "heartbeat" message to OPQHub to indicate that it is connected and functioning. This message normally includes low resolution voltage and frequency data.

When a power quality disturbance is detected by OPQBox, it sends a message to OPQHub that includes high resolution voltage and frequency data.

We plan for OPQBox timestamp data to be synchronized to within 1 millisecond, though we are currently experimenting to determine the best technique to accomplish this. Synchronization enables data from multiple OPQBoxes to be used to generate a global perspective on the state of the grid. As a simple example, it can enable users to determine if their event is local to their own residence or instead grid-wide.

Operational requirements

The design of OPQBox2 is influenced by our experience with the first generation OPQBox (OPQBox1). Design information about our first generation hardware is available at the OPQBox1 repository.

We performed a pilot study of our first generation hardware and software, and one of the results of this study are the following major enhancements for OPQBox2:

Changes From OPQBox1

OPQBox2 is a complete redesign from the previous generation. It replaces the voltage sensing transformer with an isolation amplifier. The sampling rate has increased from 4kSPS to up to 100kSPS. In order to keep up with the faster acquisition a dedicated ARM DSP is used to control the sampling and realtime processing. Here is a summary of component changes in OPQBox2:

OPQBox1 OPQBox2
Voltage sensing/Isolation 12V transformer wall plug transformer Isolation amplifier.
Power 12V transformer Isolated 5V AC-DC, Isolated 5V DC-DC
ADC 4KSPS 16Bit ADC 100 KSPS 16Bit ADC
Processing Raspberry Pi for processing/WiFi Dedicated ARM DSP for real time processing.
Raspberry PI for communication and configuration only.
PI can be replaced with CAN/RF/Ethernet/GSM module

PSU Design

Main power for the boarf is provided by the IRM-10-5 module. Hot side is powered via ADUM5010 chipscale isolated DC-DC converter.

ADUM5010 PSU design

Design notes:

capacitive PSU

Design notes:

Layout

PCB layout is available in the schematics folder. It is provided as a PADs Layout file, as well as gerbers and pdf/image files. This design calls for a 4 layer FR4 board, and measures 100mm by 100mm. PCB is manufactued and is undergoing testing. This device is intended as an engineering sample. We expect to go through several iterations refining the design.

Full Layout

layout

The Isolation barrier is clearly visible. Perhaps a cutout is appropriate to improve isolation?

Top copper, soldermask, and silkscreen

layout

Bottom copper, soldermask and silkscreen

layout

Safety

We have domain knowledge in measurement/DSP, but not PSU design and consumer products. From a safety perspective, we have implemented the following:

Engineering sample

We recently produced an engineering sample of this design:

Additional design documents

Summary of questions for review

Here are the issues we are most concerned about.

If you would like to meet in person or via teleconference to discuss this design, we would be happy to arrange that. If you can reply with comments to johnson@hawaii.edu, that would be great.

Thanks so much for your time!