Study on the Verification of the Calculated Harmonic Impedance

The verifications of the calculated harmonic impedances are necessary for harmonic impedance estimation. Among the existing methods of the verifications, the method, by matching the calculated background harmonic voltage with the measured voltage when the customer is out of operation, is widely used. The background harmonics can be calculated based on IEC61000-3-6 (named as the IEC method) or the superposition index. However, some researchers ignore the fact that these two methods cannot be chosen arbitrarily, otherwise, the misjudgments may occur. In our study, the nonlinear customers are classified into two categories according to the ways how they are out of operation: 1) only the harmonic source is cut off, and 2) the harmonic source and the impedance of the customer side are both cut off. Then, the differences in using the IEC method and the superposition index to match the calculated and measured background harmonic voltage are investigated. Finally, based on the properties of the two methods and the categories of the customers, a framework is proposed to accurately validate the calculated harmonic impedance. The effectiveness and reliability of the proposed framework are verified through simulation and field case studies.