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Energy Metering ICs with Active Real Power
The document describes an energy metering integrated circuit from Microchip Technology that provides active real power measurement capabilities. It features two 16-bit delta-sigma analog-to-digital converters, low measurement error over a wide dynamic range, and interfaces for driving mechanical counters and stepper motors. The document outlines the IC's functional blocks, current sensing options, and reference designs for using it in energy metering applications.
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Energy Metering ICs with Active Real Power
- 1. Energy Metering ICswith Active Real Power Source: Microchip Technology
- 2. Introduction Purpose Anintroduction to Energy metering IC with active real power Outline Feature Functional block, PoR Sigma-Delta Converter, High pass, Low pass filter Device Pin Features. Current sensing different types Energy meter reference design Content 14 pages
- 3. Features Supplies active(real) power measurement for single-phase, residential energy metering Supports IEC 62053 International Energy Metering Specification and legacy IEC1036/61036/687 Specifications Two multi-bit, DAC, second-order, 16-bit, Delta- Sigma Converters (ADCs) 0.1% typical measurement error over 500:1 / 1000:1 dynamic range Ultra-low drift on-chip reference: 15 ppm/°C (typ.) Direct drive for electromagnetic mechanical counter and two-phase stepper motors Low IDD of 4 mA (typ.) Tamper output pin for negative power indication Industrial Temperature Range: -40°C to +85°C Supplies instantaneous real power on HF OUT for meter calibration
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- 5. 16-Bit Delta-Sigma A/DConverters MCP390X consist of 16-Bit Delta-Sigma A/D used for both current and voltage channel measurements. They comprise a second-order, delta sigma modulator using a multi-bit DAC and a third order SINC filter. The delta-sigma is a waveform-oriented converter architecture that can offer both high linearity and low distortion performance throughout a wide input dynamic range. The SINC filters main notch is positioned at MCLK/256 (14 kHz with MCLK = 3.58 MHz), allowing the user to be able to measure wide harmonic content on either channel. SINC Filter Magnitude Response (MCLK = 3.58 MHz).
- 6. Power-On Reset (POR)Power-on Reset Operation This devices contain an internal POR circuit that monitors analog supply voltage AVDD during operation. The POR circuit has built-in hysteresis and a timer to give a high degree of immunity to potential ripple and noise on the power supplies, allowing proper settling of the power supply during power-up. A 0.1 μF decoupling capacitor should be mounted as close as possible to the AVDD pin, providing additional transient immunity. The threshold voltage is typically set at 4V, with a tolerance of about ±5%. The typical hysteresis value is approximately 200 mV in order to prevent glitches on the power supply.
- 7. High-Pass Filters andMultiplier / Low-Pass Filter and DTF Converter HPF Magnitude Response LPF Magnitude Response In order to remove DC offset components from the instantaneous power signal, a high-pass filter has been introduced on each channel. The cut-off frequency of the filter (4.45 Hz) has been chosen to induce minimal gain error at typical line frequencies. The MCP390X low-pass filter is a first-order IIR filter that extracts the active real-power information from the instantaneous power signal. The cut-off frequency of the filter (8.9 Hz) has been chosen to have sufficient rejection for commonly-used line frequencies.
- 8. Device Pin FeaturesCurrent Channel (CH0-, CH0+) CH0- and CH0+ are the fully differential analog voltage input channels for the current measurement, containing a PGA for small-signal input, such as shunt current sensing. This corresponds to a maximum differential voltage of ±470 mV/GAIN and maximum absolute voltage, with respect to AGND, of ±1V. Up to ±6V can be applied to these pins without the risk of permanent damage. Voltage Channel (CH1-,CH1+) CH1- and CH1+ are the fully differential analog voltage input channels for the voltage measurement. The linear and specified region of these channels have a maximum differential voltage of ±660 mV and a maximum absolute voltage of ±1V, with respect to AGND. Digital VDD (DVDD) DVDD is the power supply pin for the digital circuitry within the MCP devices. This pin requires appropriate bypass capacitors and should be maintained to 5V ±10% for specified operation.
- 9. Device Input PinFunctionalities Analog VDD (AVDD): AVDD is the power supply pin for the analog circuitry within the MCP devices This pin requires appropriate bypass capacitors and should be maintained to 5V ±10% for specified operation. Frequency Output (FOUT0, FOUT1): FOUT0 and FOUT1 are the frequency outputs of the device that supply the average real-power information. The outputs are periodic pulse outputs, with its period proportional to the measured real power, and to the Fc constant, defined by F0 and F1 pin logic states
- 10. Current Sensing AndDynamic Range Requirements Current-Sensing Shunt: The current-sensing shunt is a small piece of metal (typically made of manganese and copper) that is manufactured with a variety of mounting holes and wired connections. It acts as a simple resistor, with the voltage drop across it proportional to the current flowing through it. CURRENT TRANSFORMER (CT) The current transformer is another choice for sensing current when designing an energy meter The CT can handle higher currents than the shunt, while consuming less power. the trade-off is cost and, in some situations, accuracy. The non-linear phase response of the CTs causes power and energy measurement errors at low currents, with large power factors.
- 11. MCP3905A/06A Energy MeterReference Design The MCP3905A/06A Energy Meter Reference Design PCB has the following features: • Protection for IEC62053 Energy Meter EMC Immunity Tests • On-Board DC power supply • Resistor divider circuit for single-point meter calibration • Connections for current-sensing shunt or other current sensing element • Connection for voltage-sensing and power supply biasing • Connections for mechanical counter and calibration output • Low-noise PCB layout for small-signal conversion and IEC62053 accuracy compliance for small shunt values • Low-cost design
- 12. Stand-Alone MCP3905A EnergyMeter Photograph of Complete, Stand-Alone MCP3905A Energy Meter This reference design can be used as either a stand-alone mechanical counter energy meter, or as the analog front-end design in advanced microcontroller-based meter designs. The AFE design limits the overall meter accuracy. A low noise, proven AFE circuit and layout is still required for a high-accuracy meter. For both meter types, the current sense input, voltage sense input, calibration scheme, jumper selection and power supply design blocks described here should apply
- 13. MCP3905 Energy MeterEval Board MCP3905 Evaluation Board
- 14. Additional Resource Forordering MCP390X, please click the part list or Call our sales hotline For more product information go to http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=11029&mid=11〈=en&pageId=79 Visit Element 14 to post your question www.element-14.com For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility Newark Farnell
Editor's Notes
- #2 This is a training module on Microchip Energy Metering ICs with Active Real Power
- #3 Welcome to the training module on Energy Metering ICs with Active Real Power . This training module gives you a brief introduction to Energy meter ICs with Real power measurement.
- #4 The MCP3905 and MCP3906 devices from Microchip Technology Inc. are two fully functional, stand-alone energy-measurement ICs that output average and instantaneous real power. They are highly accurate solutions for single-phase energy measurement in residential power meters and industrial applications. The MCP390X energy-measurement ICs address the growing market for electronic-based energy meters, particularly in worldwide emerging markets. The new chips each integrate two 16-bit delta-sigma analog-to-digital converters (ADCs), an internal voltage reference, plus all of the digital circuitry needed to calculate average and instantaneous real power from voltage and current channels. The MCP3905 features a programmable gain amplifier (PGA) with a maximum gain of 16. For energy meters requiring higher accuracy, the MCP3906 has a maximum gain of 32. In addition, these solutions meet or exceed the requirements of the International Electro technical Commission IEC62053 international energy-metering specifications.
- #5 The MCP3905A/05L/06A devices are energy metering ICs that supply a frequency output proportional to active (real) power, and higher frequency output proportional to the instantaneous power for meter calibration. Both channels use 16-bit, second-order, delta sigma ADCs that oversample the input at a frequency equal to MCLK/4, allowing for wide dynamic range input signals. A Programmable Gain Amplifier (PGA) increases the usable range on the current input channel (Channel 0). The calculation of the active power, and the filtering associated with this calculation is performed in the digital domain, ensuring better stability and drift performance. Two digital high-pass filters cancel the system offset on both channels such that the real-power calculation does not include any circuit or system offset. After being high-pass filtered, the voltage and current signals are multiplied to give the instantaneous power signal.
- #6 The ADCs used in the MCP3905A/05L/06A for both current and voltage channel measurements are delta sigma ADCs. They comprise a second-order, delta sigma modulator using a multi-bit DAC and a third order SINC filter. The delta-sigma architecture is very appropriate for the applications since it is a waveform-oriented converter architecture that can offer both high linearity and low distortion performance throughout a wide input dynamic range. The clocking signals for the ADCs are equally distributed between the two channels in order to minimize phase delays to less than 1 MCLK period
- #7 This devices contain an internal POR circuit that monitors analog supply voltage AVDD during operation. This circuit ensures correct device startup at system power-up and system power-down events. The POR circuit has built-in hysteresis and a timer to give a high degree of immunity to potential ripple and noise on the power supplies, allowing proper settling of the power supply during power-up. Once a power-up event has occurred, an internal timer prevents the part from outputting any pulse for approximately 1s, thereby preventing potential meta stability due to intermittent resets caused by an unsettled regulated power supply.
- #8 The active real-power value is extracted from the DC instantaneous power. Therefore, any DC offset component present on Channel 0 and Channel 1 affects the DC component of the instantaneous power and will cause the real-power calculation to be erroneous. In order to remove DC offset components from the instantaneous power signal, a high-pass filter has been introduced on each channel. The MCP3905A/05L/06A low-pass filter is a first-order IIR filter that extracts the active real-power information from the instantaneous power signal. The output of the low-pass filter is accumulated in the digital-to-frequency converter. This accumulation is compared to a different digital threshold.
- #9 This page describes the current channel, voltage channel, and digital input.
- #10 This page is in continuation to previous page describing about the analog supply pin, and frequency output pin.
- #11 This page gives you an overview about the current sensing methods. Shunt type and Current transformer connecting types.
- #12 The MCP3905A/06A Energy Meter Reference Design is a stand-alone, single-phase residential meter design for active-energy meter designs. For advanced microcontroller-based meter products, this design also serves as the design of the Analog Front-End (AFE). This design includes a low-cost DC power supply circuit and the necessary protection for IEC62053 EMC compliance.
- #13 This reference design keeps all of the major components on the back-side of the PCB. This minimizes any ill effects from the environment in the situation that a meter case experiences failure. Only the necessary components for calibration, jumper selection and external connections are placed on the front-side of the board. Keeping the larger DC power supply components on the back-side of the board is also necessary for installation in some meter cases with PCB standoffs.
- #14 This evaluation board is designed to test out a variety of energy meter designs. On the input side high-voltage line and load AC-plug headers are included, along with mounting holes for shunts, current transformers and screw-type connections for wiring. On the output side a large prototype area is included along with optical isolation and a standard PIC tail header for experiments with a variety of PIC MCU-based energy meter designs.
- #15 Thank you for taking the time to view this presentation on “Energy Metering ICs with Active Real Power ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Microchip Technology site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.