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System Description
1 System Description
1.1 End Equipment
Electricity meters
and
Power quality meters
in compliance with IEC and ANSI standards. The energy measurement is the basic functionality for both and
calculates various metrology parameters. Some of the parameters are included in the following list:
•
Total and per-phase active (kWh), reactive (kvarh), and apparent energy (kVAh) with pulse-generation
outputs
•
Total and per-phase active (kW), reactive (kvar), and apparent power (kVA)
•
Per-phase voltage and current root mean square (RMS)
•
Line frequency
Typical sensors used are either current transformers (CT), shunts, or Rogowski coils.
In addition, multiple power quality parameters in a polyphase energy measurement system can be also
calculated, including:
•
Per-phase voltage total harmonic distortion (THD)
•
Per-phase current THD
•
Voltage phase-to-phase angle
•
Per-phase zero crossing
TIDA-010243 is a Class 0.1 high-accuracy 3-phase CT electricity meter reference design, using a single
8-channel standalone
ADS131M08
be used for energy metering in popular products such as Level 2 EV chargers and AC wallboxes.
1.2 Electricity Meter
Utility providers and their customers are driving the need for more features from electricity meters. Advanced
features, such as harmonic analysis, are increasingly being required from meters which mandates higher
processing and accuracy requirements for the MCUs. As an example, adding harmonic analysis capabilities
to an electricity meter can require an increase in the sample rate of the meter to capture the desired frequency
range. Often such increases in sample frequency must be done without compromising on accuracy, while the
higher sample rate, in turn, also requires more processing.
As both the accuracy requirements and amount of processing expected from electricity meters rapidly
increase, it becomes more and more difficult to solve this with a single metrology system on chip (SoC). A
common solution to this problem is to utilize a dual-chip approach with a standalone ADC and a standard
host microcontroller (MCU). Using an accurate state-of-the-art standalone ADC typically has the following
advantages:
•
Enables meeting the most stringent of accuracy requirements
•
Enables meeting minimum sample rate requirements (without compromising on accuracy) that cannot be
obtainable with application-specific products or metrology SoCs
•
Enables flexibility in selecting the host microcontroller, because the MCU only needs to meet the application
requirements, such as processing capability, minimum RAM and Flash storage for logging energy usage, and
microcontroller security features for ensuring meter data security
To properly sense energy consumption, voltage and current sensors translate mains voltage and current to a
voltage range that an ADC can sense. To sense the energy consumption when a multiphase distribution system
is used, it is necessary for the current sensors to be isolated so the sensors can properly determine the current
drawn from the two different lines without damaging the ADC. As a result, current transformers, which inherently
have isolation, have historically been used for the current sensors for split-phase, two-phase, and three-phase
electricity meters.
In this reference design, Class 0.1 three-phase CT-based energy measurement is implemented by using a
standalone ADC device, which senses the mains voltage and current. When there are new ADC samples
available, the host MCU communicates to the standalone ADC via SPI bus to read out the new samples and
calculate multiple metrology parameters. In addition, the host also communicates to a PC GUI through either the
isolated RS-232 circuitry or isolated RS-485 circuitry on the board. As an additional safeguard, an external SVS
2
Cost-Effective, 3-Phase CT Electricity Meter Reference Design Using
Standalone ADC
are two popular system designs for accurate energy measurement
ADC and cost-effective
MSPM0G3507
Copyright © 2023 Texas Instruments Incorporated
MCU. The reference design can also
TIDUF25 – JUNE 2023
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