Influence Of Current And Voltage Harmonic Distortion On The Power Measurement Of Led Lamps And Luminaires

Specific issues appear in the measurement of the electrical power of AC-powered LED lamps and luminaires because they often generate harmonic currents in a wide frequency range. The topic of this paper is to clarify the impact of these harmonic currents on the measurement of the active power. When high frequency currents are generated in an electrical circuit, the resulting voltage, current and power become very sensitive to the bandwidth of the measurement devices and to the impedance of the power supply circuit (source impedance). In this paper, several expressions of the error terms in the active power are established as functions of the total harmonic distortion figures of the AC current and the voltage. An experimental set-up was designed to compare the active power measurements performed with different source impedances and different bandwidths on an LED lamp generating high frequency harmonic currents. The active power was typically underestimated by about 3% when the measurement bandwidth was limited to 2 kHz, the IEC-61000-3-2 limit for measuring the power of lighting equipment. Similarly, deviations of about -6% appeared with increasing source impedances.