Comparison Between Quality Index and Total Vector Error Metric for Power Quality Measurements

The power grid is transforming due to an increasing share of participants connected to the grid via power electronics. This results in a degradation of the power quality (PQ) and dynamic stability leading to a rising necessity of power quality measurement. The power flow analysis is performed by phase measurements on the fundamental frequency, while harmonic phase measurements would also allow this for harmonic components. Due to the permanent decrease in power quality, this must be permanently analyzed. The quality can be defined via the Total Vector Error (TVE). One problem with the TVE is that it can only be calculated if a reference signal is available, which is not the case for field measurements. Therefore, a quality index (QI) was presented in earlier publications, which can be calculated without a reference signal. The application of the QI has proven to be difficult in previous measurements, as it behaves differently when applied to signals depending on a number of disturbance variables. It is therefore difficult to determine a specific threshold, as different thresholds are acceptable for each environment. To solve this problem, we introduce new metrics to evaluate what type of error will cause the QI to drop and a metric to estimate the TVE based on the QI and the type of disturbance identified. This has the advantage that with the TVE there are well-defined thresholds for certain applications, which can then be applied by measuring the QI and estimating the TVE on the fly.