IEC TS 62578-2015 pdf free download – Power electronics systems and equipment — Operation conditions and characteristics of active infeed converter (AIC) applications including design recommendations for their emission values below 150 kHz.
4.2.4 Filters
The supply side filter is usually designed to let the desired harmonics pass through the filterand to mitigate the undesired harmonics to a value prescribed by the EMC specifications ofthe environment. lf necessary, additional filter measures may be applied.
Additional design criteria may result from the power-supply system conditions at the lPC aswell as from economic constraints.
lt should be noted that the frequency of the undesired harmonics is mainly from pulsefrequency on upward.The specification of the converter-side filter inductor has to take thesehigh frequencies into account, otherwise the inductor will overheat.
The d.c.-side filter, if used, has to attenuate the ripple of the d.c. voltage or current so that theconverter and the possibly connected devices function properly.The specification of the d.c.-link filter has to take the amount of harmonics into account, otherwise it may overheat
ln some cases the energy-storage capability of the d.c.-side filter is adapted to the dynamicrequirements of the application.One application is the ride-through (continue operation duringand after a short interruption of the power supply network).Rapid changes of the energy flowin the power supply network or the load during power transients also need larger d.c.sideenergy storage elements otherwise the characterising d.c.-link quantity (voltage or current)may leave the tolerance band in which proper operation of the PWM converter is guaranteed.An overshoot of voltage or current, even for a very short time,may destroy the semiconductorvalve devices of the converter.
For the fundamental frequency and the controllable harmonics, the supply-side filter may beregarded as purely inductive. Depending on the topology and the chosen control principle, thevoltage drop across the total impedance drives the supply-side current.
The total impedance should be limited to allow proper dynamic control of the supply sidecurrent.
4.2.5Pulse patterns
The selected pulse pattern generation scheme greatly influences the characteristics of theconverter.The three main basic pattern generation schemes are space vector modulation,optimized synchronous pulse-width modulation and line flux guidance.
NOTE Space vector modulation and symmetric pulse width modulation lead to identical pulse patterns.
ln case of space-vector modulation a sequence of zero states and non-zero voltage spacevectors is selected in such a way that the voltage space vector requested by the controlresults as a mean value of the sequence. The zero states selected have to be of equalduration.
In case of symmetric pulse-width modulation,a set-point curve is compared to a triangularreference function.Two ways of treating the set-point curve are known:
natural sampling directly compares the (analogue) curve to the triangular reference function;
regular sampling samples values of the set point curve at the extreme values of thetriangular function and compares these sampled values to the reference function.
Digital controllers normally use regular sampling. The difference between the two methods issmall but leads to slightly different generated harmonics.
A suitable instantaneously defined zero-sequence component added to the reference values assures equal zero-state duration. This is sometimes called “addition of multiple of third order harmonic”. If the half value of the mean of the three phase signal is added to all signals, the result is identical to space vector modulation.IEC TS 62578 pdf download.