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Reflection Phenomenon in inverter fed motor

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kappa_am

kappa_am

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Hi all,
I have a question about reflection phenomenon in inverter-fed motors with long cable; I know the severity of the phenomenon is dependent on the magnitude of voltage stair (for two-level inverter it is VDC (DC link voltage) ) and the rising and falling time of the voltage. My question is that does switching frequency (carrier frequency of PWM) have any effect on exacerbation or soothing this phenomenon? if yes, how?

Thank you
 

"reflection phenomenon" doesn't sound like a commonly understood technical term related to inverters. I have only a vague idea what you are talking about.
 

This phenomenon also occurs in transmission lines when a circuit breaker turns ON. when a wave travels through a long line, at the end it reflects back, so the voltage at the end of the line would be almost two times of wave magnitude. This penetrate to motor windings and damages motor winding's insolator. To solve this problem dv/dt filter is usually used at the inverter output, or by multilevel inverter we can reduce amplitude of the switched waveform.

I'd like to know if the magnitude of the phenomenon depends on carrier wave frequency? I couldn't manage to figure it out using traveling wave relations.
 

It doesn't depend on switching frequency. Transient voltage increase at the far end occurs if the cable propagation time is at least in the same order of magnitude as voltage rise time at the inverter terminals. With maximum 10 or 20 kHz switching frequency, the reflections completely decay between switching edges.

All inverter manufacturers require output filters for inverters above a certain motor cable length.
 

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