Harmonic distortion and oscillatory voltages and the role of negative impedance

This paper focuses on two power quality effects that are noticed with power electronic appliances. One effect is a harmonic oscillation by inverters of photo voltaic systems because they bring a high parallel capacitance to the grid and negative output impedance. The other effect is a sub-harmonic oscillation due to the negative differential impedance of constant power loads. This paper discusses both effects and proposes counter measures to mitigate these effects. For harmonic oscillations due to photo voltaic inverters, an extra feature for these inverters is discussed. For the sub-harmonic oscillatory voltages due to appliances with negative differential impedances, a solution can be found in the voltage control systems of the power generators connected to the network.