Measurement Computing WavePort 312P rev.1.0 - Manual (Page 75)

PowerVista/312 User’s Manual Frequency Following 10-1
10 Frequency Following
10.1 Frequency Following Overview
Frequency Following is an EasyPower Measure expert algorithm used to convert samples occurring at a fixed
sample rate to a set of samples that always contain a fixed number of points within a single fundamental cycle.
This operation has historically, and still is on most power system instrumentation, been performed via a
hardware phase locked loop. The hardware senses the frequency of the synchronizing phase (normally Phase 1)
and outputs a clock signal to sampling hardware so that a fixed number of samples is always captured on a given
cycle. This method, though very successful, does have certain limitations in response time to sudden changes in
frequency, and limited ranges for frequency excursion. Specialty hardware is needed to facilitate a phase locked
loop for frequency following. Such hardware is not found on generic sampling hardware within the present
market.
EasyPower Measure Frequency Following was by nature designed to remove the need for specialty hardware
so that power system measurements can now simply be a matter of appropriately applied algorithms in software.
Dedicated specialty hardware is no longer needed. As long as a hardware platform has adequate fixed sampling
speeds, throughput, and accuracy, frequency following can be implemented. As a side benefit, software
frequency following opens the constraints within present frequency following techniques. Since following
occurs in software, setting a base system frequency is merely a matter of an input data change. The EasyPower
Measure definition of Base Frequency in the System Configuration is that data item. It is the only input data
item needed as the algorithm is self contained and performs following on any input frequency from
10 to 500 Hz.
10.2 Frequency Following Application
Applying Frequency Following is simply a matter of enabling it within the software and supplying a properly
specified Base Frequency. Once enabled, all RMS and phasor calculations will be performed after their input
waveforms have been modified according to input frequency. Frequency Following is simply a front end
algorithm that pre-processes wave data before it is used to perform calculations. A simplified flow chart has
been supplied
in Figure 10-1 .
Figure 10-1. Application of Frequency Following.