Passive grid impedance estimation using several short-term low power signal injections

In this paper, a method is proposed for passive grid impedance estimation using several short-term low power signal injections. Impedance estimation is used in many applications such as designing filters and stable inverters. In impedance estimation techniques with signal injection, a voltage signal is applied to grid and the division of voltage to current signal in frequency domain is considered as the impedance. Accuracy of impedance estimation in noiseless systems is independent to energy of injected signal. But in noisy system, energy of injected signal must be sufficient for an accurate approximation. In this paper, our simulation error is additive white Gaussian noise which is considered as measurement noise. The injection signal is ideal impulse or short duration rectangular pulse. Energy of the rectangular pulse dependents to the peak amplitude and pulse width. In low voltage power grid systems (220v), the peak amplitude of injecting signal is limited up to 2kv. In addition, increasing the pulse width reduces the bandwidth of the signal. Accurate impedance estimation using signal injection can be done in frequencies with sufficient energy and therefore every rectangular pulse can estimate impedance in some frequencies. In this paper, a method for passive grid impedance estimation based on combination of several signal injections is proposed. The simulation results show that the proposed method can properly estimate grid impedance in a wide frequency range up to 10kHz.