A Digital Heterodyne 2- To 150-kHz Measurement Method Based on Multiresolution Analysis

A description is given of a new 2- to 150-kHz range frequency decomposition method, as required to support power grid compatibility level measurements. This real-time digital method is based on a tree structure of nominally identical modular algorithmic elements to provide a decomposition of the signal bandwidth resulting in a 200-Hz resolution. Each modular element divides the bandwidth of its input into a low-frequency and a high-frequency half. Elements connected in the tree result in a progressive increase in resolution at each level of the tree, hence multiresolution analysis. The modular element is based on heterodyning and down-sampling. Simplifications of the modular elements that result in an efficient process of changing the sign of alternate input samples, digital filtering, and discarding alternate samples at the output are presented. It is shown that these cloned modular elements form a computationally efficient algorithm that can operate in real-time. Refinements to cover gaps in the bandwidth which cause errors are explained. The algorithm is compatible with the traditional CISPR 16 analog heterodyne method. Test results are presented which show that the method achieves accuracies of ±5% of reading, as required for compatibility level measurements.