A novel grid impedance estimation technique based on adaptive virtual resistance control loop applied to distributed generation inverters

Abstract

The penetration of the distributed power generation systems (DPGSs) based on renewable sources (PV, WT) is strongly dependent on the quality of the power injected to the utility grid. However, the grid impedance variation, mainly caused by grid faults somewhere in the electric network, can degrade the power quality and even damage some sensitive loads connected at the point of the common coupling (PCC). This paper presents detection-estimation method of the grid impedance variation. This estimation tehnique aims to improve the dynamic of the distributed generation (DG) interfacing inverter control and to take the decision of either keep the DG connected, or disconnect it from the utility grid. The proposed method is based on a fast and easy grid fault detection method. A virtual damping resistance is used to drive the system to the resonance in order to extract the grid impedance parameters, both resistive and inductive parts, using resonant filter frequency determination. Theoretical analysis and simulation results are presented to validate the proposed method.

Operation and Control of an Improved Performance Interactive DSTATCOM

“…for the lowest possible value of the load power, then it is valid for all other loads. Eventhough this scheme does not require knowledge of source impedance throughout the DSTATCOM operation, several schemes for online grid impedance measurement have been available [23]- [27].…”

Grid impedance estimation based hybrid islanding detection method for AC microgrids

“…For this reason, active damping is adopted as a solution and it is carried out by implementing a virtual resistance in the control strategy. In fact, it is done by multiplying the sensed filtercapacitor current by a predetermined gain noted R v [3], and the result of this multiplication is subtracted from the converter voltage reference as depicted in Fig. 3.…”

“…However, unplanned islanding, that is to say the failure of the grid, is more complicated to be detected since the voltage and frequency at PCC can be sustained in NDZ limits. In the literature, several methods have been proposed for islanding detection due to the importance of this issue and its impact on the interconnected system behavior [19,1,14,3,8,6]. These methods are mainly divided into two main categories: communication-based methods between the protection devices and the power generation system, and local methods that use only local measurements.…”

“…This resistance helps, in grid connected mode, to improve the output power quality in healthy grid mode and to drive the system near the resonance once an abrupt grid current variation is detected. It also allows the discrimination of the variation causes: grid impedance variations [3] or load variation. This method is able to detect islanding conditions under any faulty condition even under the NDZ, the worst case, where other methods failed [8].…”

Impedance computation for power electronic converters with Hilbert transform

“…Moreover, some tests use the frequency analyzer devices to obtain the impedance in the frequency domain [14]. Additionaly, some estimation techniques, in this case for grid impedance equivalent, have been presented in [15], [16]. Reference [12] stated that the use of sinusoidal current/voltage sweeps to compute the impedance is the most reliable and accurate method and that this is not suited for online measurements due to the measurement time.…”