DAQ SoCs improve smart grid monitoring & protection

5th November 2015

Analog Devices

Barney Scott

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Analog Devices has introduced a 24-bit Data AcQuisition (DAQ) SoC series designed to improve the performance of protection, monitoring, and power quality measurement equipment used to manage transmission and distribution of energy within smart grids. All three devices in the AD777x series offer the industry’s best combination of dynamic range and data throughput and feature eight simultaneous sampling channels that measure the output from current and voltage sensors in three-phase power applications.

The AD7770 enables higher performance and smaller form factor protection relays, while the AD7771 enables power quality measurement equipment to provide early detection of power grid electrical faults. The third SoC in the series, the AD7779, ensures fast power-up in circuit breaker equipment.

Each SoC channel achieves 112-dB of dynamic range at 8kSPS, enabling the consolidation of protection and measurement functions on a single ADC channel. The AD777x series also includes an integrated sample rate converter, which simplifies the design challenge associated with making the power quality equipment compliant with the IEC61000-4-30 Class A standard.

The AD777x series incorporates a PGA to scale various sensor outputs, allowing system designers to use a common platform for applications with different accuracy requirements and input sensor types, including current transformers, potential transformers, and resistive strings. Additionally, the AD777x series lowers total system cost by eliminating the need for external components such as signal conditioning amplifiers and PLLs. The entire AD777x series incorporates sample rate converters that enable the fine adjustment of the sampling rate and maintain coherency to a 0.01Hz change in line frequency over a 50Hz (-15%) to 60Hz (+15%) range. This is a requirement for the IEC61000-4-30 Class A power quality standard.

The devices also incorporate a number of on-chip diagnostic features that ease the design process for end-equipment SIL certification. An additional low-resolution SAR ADC channel operates from a separate power supply and provides data for system and chip diagnostics, improving confidence in data integrity and boosting overall system reliability. The AD7771’s high dynamic range, coupled with a high sampling rate, enables the reduction of the Fast Fourier Transform (FFT) noise floor. This enhances the detection of abnormal frequency spurs, which can signal a developing electrical fault, and enables early warning detection and preventative maintenance by power quality measurement equipment.

All three devices are offered in 64-lead LFCSP packages and scheduled for production in early 2016. The AD7779 will be priced at $5.90, the AD7770 at $6.97 and the AD7771 at $7.94, all per unit in 1,000 unit quantities.