By Pavel Mihatsch
Briefly put: As more elements are added into the grid, power quality standards and measurement need.
The situation on the low voltage grid has significantly changed over the past few years. This comes as a result of the arrival of new appliances – lights, electronics with switched-mode power supplies – and due to the changes at supply/generator sites.
Power supplies – a lot of small players
In the past, big generators (rotating machines) were predominantly used. Their construction led to the direct generation of a sinus curve. Their distortion came as a result of technical (electric and mechanical) imperfections, and was very small. Today, large amounts of small, nonrotating generators are in the field – they are switched-mode inverters/converters. In order to generate pseudo sinusoid curves, pulse-width modulation (PWM) with low-pass filter is used. Modulation frequency reaches several kHz. Principally, PWM generates plenty of higher harmonics, which should be filtered from the final signal. However, filtration of these harmonics brings higher financial costs, and it is thus, in most cases, tolerated. The higher power generated supplied, the more complicated and expensive the filtration (coil and capacitor) to be used. Subsequently, this leads to a power supply quality aggravation.