Current sampling and measurement in PWM operated AC drives and power converters

Current regulation is an essential part of many AC drives and power converters, with fast and accurate measurement of the current being essential for this purpose. High frequency harmonics, which are always present in power converter systems, can produce aliasing phenomena if the signals from the current sensors are not adequately processed and sampled. Synchronous sampling is a mean to reduce the risk of aliasing without the penalties that are intrinsic to other methods, e.g. phase-lag when using anti-aliasing filters. However, the performance of synchronous sampling does not always meet expectations, depending on the converter´s design, operating characteristics and operating conditions, which can compromise the performance of the current control. This paper analyzes the various methods for current sampling and measurement in AC drives and power converters with particular attention paid to the performance and limits of synchronous sampling.