RESI – Resonance Elimination Systems

Introduction: Theoretically, AC voltage from the mains has a perfect sine wave. In practice, real loads cause deviations, called harmonic voltage distortions, whose frequency are integer multiples of the fundamental frequency. This effect has been well known for a long time, as have the corresponding countermeasures. In recent years, however, other distortions of the voltage waveform have increasingly been placing a burden on the grids. For example, self-controlled power converters of all types feed higher-frequency voltage distortions (supra-harmonics) into the grid with the clock frequency of the power electronics. With the multitude of non-resistive loads, there are also increasingly pronounced interactions. Resonances can thus hardly be predicted.

The effect is known from simple physical experiments with oscillating systems: A simple electrical circuit consisting of a capacitor and a coil exhibits a certain natural frequency. The phenomenon also exists in mechanics in the form of a pendulum. Such systems are easy to calculate. However, if several of them are coupled, their behaviour is practically impossible to predict. Even a simple double pendulum is a non-linear, dynamic system; its movement pattern is chaotic. Such couplings are also becoming increasingly common in electrical networks: Long cable runs, input filters of converters, etc. form a resonance together with the feeding transformer. Even unchoked compensation systems, which are actually supposed to stabilize the grid, can contribute to resonances. The more potential partners are connected in a network, the higher the probability that resonances will occur. They can create serious and sometimes destructive overvoltages. Pure LC suction circuits cannot eliminate these resonances, but only shift them in frequency.

In such cases, the systems from the RESI product family provide a remedy. Thanks to an attenuated high-pass filter, they can eliminate both higher frequencies (supra-harmonics) and mains resonances. RESI systems are scalable. The product family includes compact stand-alone units up to large units that efficiently attenuate transients, clock frequencies and commutation dips of high-power converters.

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