LED Testing - Efficiency and Power Quality Analysis

Introduction

As LED light applications are quickly replacing incandescent light bulbs and energy-saving lamps, due to their high efficiency and extended lifetime, using Dewesoft data acquisition technology we dive deeper into this technology to put it to the test, as we test multiple led products. 

The questions we asked ourselves: Is the efficiency as good as proclaimed in a standard electrical system? As well as what are the Power Quality effects that materialize in LED lighting devices, and what effect do they have on power systems with the European nominal voltage of 230 V, without the use of any additional power conditioning? 
 
The measurement is broken down into two measurement segments for lighting below 25 Watts: 

• In the first segment, the third and fifth harmonics and the associated waveforms are evaluated to determine if an LED light bulb meets the requirements set by the standard for light-emitting diodes by comparing the deviation from the ideal sine waves. 

• In the second segment, the individual harmonic currents are compared to the limits of Class C classified equipment in the IEC 61000-3-2 Standard. 

The problem and measurement application

LED light bulbs are more energy-efficient than incandescent bulbs, but they also have some disadvantages. As we are using a light-emitting diode that produces a non-linear load, they can impact the power quality negatively, by introducing noise into the grid. This puts unwanted strain on the AC circuit.

As more and more LED-based lighting systems are utilized, the power quality of the electrical network can be influenced negatively which in turn causes undesirable power quality values and poor power values in the grid.

We will describe the methods for using the Dewesoft power quality analyzer for precise and convenient power quality monitoring and the measurement of these detrimental effects. 

Measurement and test setup

LEDs are powered by a DC line generated by a switching power source. For the DC power analysis, a data acquisition system with high bandwidth and a high sampling rate are necessary due to the high switching frequencies of the ballast units or switching regulators in fluorescent lighting and LEDs. 

The Dewesoft SIRIUS HS (High Speed) amplifiers fit perfectly into this application and allow a completely synchronous efficiency analysis of the full energy flow (AC power, DC power, luminance).

The SIRIUS HS series DAQ system was chosen for this measurement as it combines high bandwidth with alias-free signal acquisition with the possibility to measure with a sample rate of up to 1 MS/sec. The Dewesoft DAQ devices are designed to be fully modular, meaning that multiple devices can be used simultaneously, measuring different parameters with all channels fully synchronized to each other.

The SIRIUS DAQ system is also fitted with an anti-aliasing filter that can be combined with an infinite impulse response filter (IIR) inside the field-programmable gate array (FPGA). These filter solutions are standard and can be activated or deactivated by the user as required. 

On one hand, the Low Voltage amplifier (SIRIUS HS-LV) in combination with the 16-bit ADC technology allows for measurements of very low voltages even at high measurement ranges (e.g. µV resolution at a range of ± 10V). These voltage levels can be set in the measurement setup in Dewesoft X.

On the other hand, the High Voltage amplifier (SIRIUS HS-HV) allows the direct measurement of voltages up to 1600V DC. This ensures that the grid voltage, in this case, could be directly measured with the built-in amplifiers without any additional voltage transducers. 

The DS-CLAMP-150DC is a current transducer that is based on the Hall effect, which measures the flow of current using the magnetic field that is created around the conductor. The current flow is directly proportional to the voltage output. It also has the advantage that the measurement is galvanically separated, making the measurement much safer. 

The Hall effect is conveniently used to measure both the AC and DC currents with a wide amplitude and frequency range (up to 100 kHz) with high sensitivity and good accuracy of 0,5% of reading. For this reason, it is recommended to use hall effect-based clamps to measure DC currents. 

The DewesoftX data acquisition software that is used is very intuitive as well as user friendly, and in combination with the power, the module makes this type of measurement precise and easy. 

The power analysis module is one of the most complex mathematical modules in Dewesoft X. It allows measurements of direct current and alternating current grids operating at different frequencies with a variety of pre-installed wiring configurations and even variable frequency sources. All the measurements are completely synchronous.

The pre-installed wiring schematics available in the DewesoftX power analysis module are as follows:

• DC

• Single-phase

• 3-Phase Star

• 3-Phase Delta

• 3-Phase Aron 

• 3-Phase V

• 2-Phase

• 3-Phase 2-meter

For this measurement, the DC and Single-Phase AC wiring schematics were selected. From a dropdown list in the schematic set-up page, the channels can be assigned to the corresponding measurement lines. 

The following image shows the waveforms of the AC (left) and DC (right) of an LED, as well as the wiring schematic that was used to do the measurement. The raw data storing capability also allows for Transient recording or a dU/dt analysis as seen on the DC side. 

The LED in figure 1. has a DC to AC efficiency of 80 %. The active power is 5,3 Watts. According to the energy labelling this LED will have:

• Class A Efficiency

• 5,3 kWh/1000 hours energy consumption

The LED seems to be the best choice due to its unquestionably high energy efficiency. However, the question remains LED is indeed the best technology to use with little to no detrimental effects.

When analyzing the AC waveform that is being delivered from the grid on the left-hand side of the image above, it is clear that the current waveform is no longer sinusoidal, meaning that the power factor will be lowered. There is also a large amount of distortion which influences the grid negatively.

There is a lot of distorted power present which affects the quality of the power grid and causes poor power quality.

All electrical devices must fulfil requirements for harmonic currents which are defined in the IEC 61000-3-2 standard. The limits for Lighting are defined in Class C. Lighting is split into two regions of the rated electric power the first is lighting under 25 watts, and the rest fall in the segment over 25 watts.

Measurements

For lighting below 25 watts, there are three possible procedures to perform the tests. We will be discussing two of these in this application note.

Procedure 1 - third and fifth current harmonic analysis

The first procedure analyses the current harmonics of the third and fifth harmonic order, as well as analyses the waveform of the current within one period.

Harmonic currents limits

When the waveform is analyzed, the peak value of the current must appear at a phase of ≤65° and should not fall below 5% before it reaches the 90° phase.

If we now analyze the waveform of the LED under test, it is quite clear that it does not fulfill this prerequisite at all. The harmonic currents for I_H3 and I_H5 exceed the set limits and the waveform characteristics are far from the requirements set by the standard. 

Dewesoft is able to perform a very quick and powerful analysis according to these requirements. In the Scope View, the waveform can be analyzed immediately with a couple of triggers and analysis functions. The harmonic currents can be verified quickly whether with the Harmonic FFT chart or the Vector Scope which is able to show each individual harmonic, in absolute values as well as percentages.

Procedure 2 - each individual current harmonic analysis

The second procedure is to analyze if the harmonic currents, without harmonic filters for each individual harmonic don’t exceed the limits of equipment as classified in Class D specified in IEC 61000-3-2:2018 (table 3, column 2 - Class D equipment, page 22):

Limits for the harmonic currents

In this case, the harmonic currents are referenced to the nominal active power of the light bulb.

Conveniently this analysis can be done in Dewesoft X software as well. With the Reference Table functionality, all harmonics and their limits can be shown within one diagram. For this LED light almost, all the harmonic limits are exceeded which lowers the economic efficiency of these lighting systems.

Results

In this measurement application, the typical power triangle:

• apparent power (S), 

• real power (P), and 

• reactive power (Q)

of the AC power analysis is not suitable. This is due to other parameters such as the distortion and harmonic reactive power that have to be considered due to the non-linear load that is caused by the LED (non-linear loads are also produced by inverters, electronic ballast units, computer power supplies, and rectified inputs, among others). 

The Dewesoft power module brings all the necessary tools to successfully measure in the non-linear field. Besides the Harmonic Reactive Power (QH), occurring through the phase shift between voltages and currents of the same frequencies a new parameter must be considered: The Distortion Reactive Power (DH).

The Distortion Reactive Power is defined as the combination of voltages and currents from different frequencies which produce the distortion power.

Although the LED technology is said to be very efficient, the tested LED creates a lot of distortion power. This is seen especially in the high distortion power (DH) and the high current total harmonic distortion (THD):

• P = 5,3W

• Q = 10,4VAr

• QH = -0,9VAr

• DH = 10,4VAr

• S = 11,7VA

• THD_I = 183 %

Conclusions

The Dewesoft Power Analyzer is able to measure both Efficiency and Power Quality as well as do a full analysis of Light Bulbs using a single instrument. This is a new and innovative lighting test experience.

Of the 10 LED light bulbs that were tested, surprisingly only one passed the Power Quality Test. The LEDs for this test were selected at random without any bias to make, modal, and price. Only after the test, these parameters were evaluated, due to data privacy regulations we cannot disclose this information at this time. 

Check of the voltage source

Before the power quality emissions of the LED bulbs can be tested, the voltage source must be checked and it must be verified that all parameters (harmonics) are within the required limits, to ensure that there are no big voltage drops or voltage sags. The IEC 61000-3-2 regulation requires that the harmonic voltages are below specified limits.

Specified limits for harmonic voltages

One big benefit of using Dewesoft DAQ instruments is the software option background harmonics (see 6.2.1. Background Harmonics in the Power Analyser Manual) where possible distortion and voltage harmonics of the grid can be compensated, and tests can be done according to the IEC 61000-3-2.

Documentation