IEC TR 61000-4-40:2020

Electromagnetic compatibility (EMC) - Part 4-40: Testing and measurement techniques - Digital methods for the measurement of power quantities of modulated or distorted signals

IEC TR 61000-4-40:2020 which is a Technical Report, deals with the assessment of electrical power quantities (RMS voltage, RMS current and active power). It explains and compares two digital algorithms suitable for power quantity measurements in fluctuating or non-periodic loads. The examples are from 50 Hz or 60 Hz power systems. This document does not attempt to cover all possible digital implementations of the algorithms used for power quantity assessment in fluctuating loads, for example in the context of the EMC assessment described in several IEC documents. Rather, it compares averaging with one of the filtering algorithms. This document aims to highlight some examples of applications that illustrate how the presented algorithms work. Further, guidance is given for quantifying the accuracy of each approach.

General Information

• Status: Published
• Publication Date: 10-Mar-2020
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 33.100.01 - Electromagnetic compatibility in general
• Technical Committee: SC 77A - EMC - Low frequency phenomena
• Drafting Committee: WG 1 - TC 77/SC 77A/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 13-Mar-2020
• Completion Date: 11-Mar-2020

Standards Content (Sample)

IEC TR 61000-4-40 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Electromagnetic compatibility (EMC) –
Part 4-40: Testing and measurement techniques – Digital methods for the
measurement of power quantities of modulated or distorted signals
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IEC TR 61000-4-40 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Electromagnetic compatibility (EMC) –

Part 4-40: Testing and measurement techniques – Digital methods for the

measurement of power quantities of modulated or distorted signals

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.100.01 ISBN 978-2-8322-7907-6

– 2 – IEC TR 61000-4-40:2020 © IEC 2020
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 General . 7
5 Modulated sine waveforms used in this document to compare measurement
algorithms . 9
5.1 General . 9
5.2 Half-wave rectification . 10
5.3 Full-wave rectification . 10
5.4 Multi-cycle symmetrical control . 11
5.5 Random on-off control . 12
6 Measurement algorithms . 12
6.1 General . 12
6.2 Averaging algorithms . 12
6.2.1 General . 12
6.2.2 Performance of the averaging algorithm . 13
6.2.3 Instrumental errors of the averaging algorithm . 18
6.3 Smoothing filter algorithm . 19
6.3.1 Frequency and step response . 19
6.3.2 Verification of the smoothing filter algorithm . 21
6.3.3 Instrumental errors of the filtering algorithm . 25
7 Conclusions . 25
Annex A (informative) Smoothing filter studied in this document . 27
A.1 Algorithm . 27
A.2 General C++ class program code . 31
Bibliography . 34

Figure 1 – Typical resistive load current and supply voltage waveform of half-wave
rectification . 10
Figure 2 – Typical full-bridge rectifier current and supply voltage waveforms . 11
Figure 3 – Current and voltage patterns in an MCSC circuit, (left) 1/3 MCSC and
(right) 2/3 MCSC . 11
Figure 4 – Amplitude of 50 Hz current with on and off periods varying within a 1 min to
2 min range . 12
Figure 5 – Step response of an algorithm in Formula (6) with a half-cycle, 1-cycle and
10-cycle measurement interval . 14
Figure 6 – RMS current and active power for half-wave rectification . 15
Figure 7 – Sliding average RMS current and active power of a device controlled with a
1/3 MCSC circuit . 15
Figure 8 – Worst case 1/3 MCSC circuit active power calculation variation . 16
Figure 9 – Example of a 10 min sliding average power calculation for a load having a
92 s period . 17
Figure 10 – Active power of randomly fluctuating load averaged over a sliding 10 min
interval . 18

Figure 11 – Sensitivity of the full-bridge rectifier RMS current and active power
measurement to time interval error of single-cycle sliding average calculation . 19
th
Figure 12 – Comparison of the first and the 10 order filters used to estimate RMS

current of a step signal . 20
Figure 13 – Filter frequency responses . 20
Figure 14 – Filter step responses . 20
th
Figure 15 – Output of the 10 order smoothing filter used to calculate the active
power of a signal with a step change . 21
th
Figure 16 – Delay and response time of a 10 order filter used to assess the
sinusoidal current of a sinusoidal waveform . 22
Figure 17 – Measurement of the current and power of a half-wave rectified signal

using a smoothing filter with a 10 Hz cut-off frequency . 22
Figure 18 – Power quantities in full wave rectification assessed using a smoothing
filter with 16,667 Hz cut-off frequency . 23
Figure 19 – MCSC 1/3 pattern power quantities filtered with approximately 5,556 Hz
cut-off frequency . 23
Figure 20 – Active power of a load having a 92 s period measured with different

algorithms . 24
Figure 21 – Active power of randomly fluctuating load measured using different
algorithms . 25

Table 1 – Calculated power of 2/3 MCSC for different measurement windows . 16

– 4 – IEC TR 61000-4-40:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMAGNETIC COMPATIBILITY (EMC) –

Part 4-40: Testing and measurement techniques –
Digital methods for the measurement of power quantities
of modulated or distorted signals

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