Power Analysis Theory and testing to IEC62301/EN50564 - PowerPoint Presentation

Slide1

Power Analysis Theory

and testing to IEC62301/EN50564Slide2

N4L PPA Series – Basics of Power measurement

Basic electronics courses teach us that power measurement, in its simplest form, is the process of multiplying voltage and current together.

This presentation will illustrate the complexities of such a measurement

and describe how N4L have overcome them

Discuss use of DSPs and the use of FPGAs to overcome real time processing constraints

Standby Power MeasurementSlide3

The Signal Chain – From Analogue input connector to instrument display

The

signal chain involves various stages including (but not limited to)

Analogue Input connections

Signal

conditioning (Attenuation + ranging)

Digitisation

Isolation

Digital Signal Processing

Data Display

Each stage needs to provide excellent accuracy, repeatability and minimal drift.Slide4

The Signal Chain - Overview

?

If we can understand how the grey box works, we have a better chance of maximising

performance of the power analyser in a real world application

Data Display

Signal ConnectionSlide5

The Signal Chain - OverviewSlide6

Analogue Input Connections

Real world applications require different levels of voltage attenuation and current measurement ranges

A Power analyser should offer a range of input connections

External Current Input (up to 3V), Internal current shunt (up to 50Arms)

External Voltage input (Up to 3V), high Voltage attenuator (3000Vpk max)Slide7

Analogue Front End – Current Shunt and Voltage Attenuator

Vitally Important that the analogue voltage attenuator/current shunt design is extremely flat with respect to frequency response

Will require less calibration and better wideband performanceSlide8

Analogue Front End Example design – Current ShuntSlide9

Current Shunt – Field CancellationSlide10

Current Shunt – Field CancellationSlide11

Current Shunt – Field CancellationSlide12

Current Shunt – Field CancellationSlide13

Current Shunt – Field CancellationSlide14

Current Shunt – Field CancellationSlide15

High Frequency Isolation – What does this mean?

In most cases, the isolation barrier between the analogue input channel and the main PCB (i.e. motherboard) provides isolation after the DSP, and computed answers are passed across the isolation barrier.Slide16

High Frequency Isolation – What does this mean?

If the raw high speed data, sample point by sample point is transmitted across the isolation barrier, an FPGA can be utilised for real time, gapless parallel processing of the data across all phases.

Resulting in phase-phase synchronicity and better phase accuracySlide17

FPGA – DSP Real Time Link

The FPGA collects the raw data samples from the analogue cards and “Double Buffers them”

The FPGA then sends an interrupt to the DSP every 16 samples

The DSP uses DMA to load them into memory for processingSlide18

Double Buffering?

Double buffering enables continuous no-gap, uninterrupted data acquisition

Allows the FPGA to

perform tasks it is best at

Allows the DSP to perform tasks it is best at

Data + Interrupt

2Ms/s

Raw Data

DMA Access

FPGA

DSP1

CPU

DOUBLE_BUFFER

DOUBLE_BUFFER

ANALOGUE CHANNEL

DSP2

FREQUENCY_DETECTSlide19

Frequency Detection

DSP2 is a dedicated frequency detection DSP

Utilises DFT to extract fundamental

Sends data back to FPGA for window synchronisation

FPGA

DOUBLE_BUFFER

DSP2

FREQUENCY_DETECTSlide20

Very different to an Oscilloscope

Oscilloscopes are not calibrated with high voltage probes

Phase is not calibrated between voltage and current

Signal chain has no “feedback”, i.e. no window synchronisation and no real time processing capability

No traceability back to ISO17025 power standards

It is a different tool for a different job.Slide21

Standby Power Measurements

When approaching a new application, the first thought should always be - What does the waveform look like?

Is the voltage sinusoidal or distorted?

Is the current sinusoidal or distorted?

Is the fundamental waveform buried within a switching carrier frequency?

What is the maximum voltage/current level?

What is the minimum voltage/current level?



If the waveform looks like this, the demands placed upon the power analyser are significantSlide22

Why is this waveform challenging?

The Voltage is relatively simple to measure (in a compliant test environment the waveform should be sinusoidal – more on that later)

The current poses the biggest challenge – it exhibits a high crest factorSlide23

High crest factor?

In standby mode, the current is often asynchronous with the voltage waveform exhibiting random pulses high in magnitude.

Many analysers will struggle to auto-range upon this waveform

It is important to use a power analyser with good dynamic range

 Slide24

Power

Analyzer

Voltage and Current connections

A small amount of current will flow through voltage attenuator

When monitoring very low power (

mW

) this can cause a large % error in the power measurement

Bad practiceSlide25

Power

Analyzer

Voltage and Current connections

The voltage attenuator current is not measured by current channel

Good practiceSlide26

EN50564/IEC62301

EN50564 States requirements of test equipment manufacturers

Provides guidance for requirements of both the Power Analyser and AC Source

Difference between “off” and “standby” can be quite subtle.

Off Mode : A condition in which the product does not provide any function other than the ability to react to a users action to “activate” or “turn on”

no automatic “cycling” into other modes takes place.

An indication LED can be lit and is not considered a function.

Standby Mode :

Activation of other modes by remote switch (such as a remote control, internal sensor or timers)

Continuous function (such as time being displayed on screen, or screen savers)

What is “Standby mode”?Slide27

EN50564/IEC62301

Network communication through network interfaces, this can include RS-232, LAN, USB etc.

PC’s (or other devices) with “Wake on LAN” capability

Sleep Mode as defined in Energy Star which maintain network connectivity such as quick restart of PC hard disks

Security alarm reactivation

Amongst others

Modes not considered as “Standby”Slide28

EN50564/IEC62301

Crest Factor (again)

EN50564 describes the likelihood of current waveform crest factors exceeding CF10 (EN50564:2011 Annex B, section B.1.2)

A

ll N4L power Analyzers offer a guaranteed accuracy specification to CF20. Furthermore, N4L Power Analyzers will auto range up without clipping of a waveform up to CF20.

All N4L Power Analyzers offer true no gap analysis at very high sample rates (PPA500/1500/3500 1Ms/s, PPA4500/5500 2Ms/s), this is a necessity for reliable measurement as standby power modes often exhibit non periodic current pulses.

If the

analyser

employ’s gapped analysis techniques these pulses can be missed and incorrectly power measurements are likely. Slide29

Current Transducer Options

If current exceeds the internal shunt maximum rating, there are a number of choices – Which one is best?

Conventional CT

Voltage output

current clamps

Rogowski

Coils

Resistive Shunts

Zero Flux CTSlide30

AC Power source RequirementsSlide31

Power Measurement Uncertainty

EN50564 refers to “Maximum current ratio”

in order to determine the power accuracy requirements

The MCR factor accounts

for the additional range errors when crest factors are highSlide32

Power Measurement Uncertainty

EN50564 refers to “Maximum current ratio”

in order to determine the power accuracy requirements

Example MCR measurement with PPA1510 and

PPALoGSlide33

Power Measurement Uncertainty

In this example, a 50mW

uncertainty level would be permitted.Slide34

Sampling methods

N4L Power analyzers utilize “Sampling method”, as preferred by EN50564Slide35

Non-Cyclic and Cyclic measurementsSlide36

Test setupSlide37

ReportingSlide38

ReportingSlide39

ReportingSlide40

Thank you for listening