Plug-In Identification Method for an <italic>LCL</italic> Filter of a Grid Converter

Abstract

This paper proposes a method for estimating the two inductances and the capacitance of an LCL filter, connected between the converter and the grid. Only the DC-bus voltage and converter phase currents need to be measured. An excitation signal is fed into the converter voltage reference. The fundamental and selected harmonic components are removed from the stored identification data to prevent biases in the parameter estimates. The parameters of the hold-equivalent discrete-time model are estimated recursively. The inductance and capacitance estimates are calculated from the estimated discrete-time parameters using the corresponding closed-form model. The proposed method can be added to existing converter control algorithms. It can provide the parameter estimates for the converter control. Further, it can be run occasionally during the normal operation in order to obtain an updated grid inductance estimate. Experimental results show that the proposed method yields very good parameter estimates and that it can also detect the changes in the grid inductance.

A Robust Circuit and Controller Parameters’ Identification Method of Grid-Connected Voltage-Source Converters Using Vector Fitting Algorithm

“…It can be seen that the identified circuit and controller parameters highly agree with the actual values in Table I. In addition, identification accuracy of LCL filter parameters based on the proposed method is higher than that proposed in [14], where the identification errors of L f 1 , L f 2 , and C f are 8%, 2%, and 12%, respectively. It is worthwhile noting that different from experimental verification, the actual parameter values are exactly known in the theoretical verification, which enables better analysis of parameters identification accuracy.…”

“…Grid-connected voltage source converters (VSCs), as the power electronic interface, are widely used to transmit the generated electrical energy into utility grid [3], [4]. It's important to know the accurate circuit and controller parameters of the VSCs to identify instability sources [5]- [9], to perform adaptive control [10]- [12], and to perform condition monitoring and fault diagnosis [13], [14]. However, subsystems of such a distributed power system are commonly provided by various manufacturers.…”

“…Various methods have been proposed to estimate or identify the parameters of the VSCs [10], [11], [13], [14], [18]- [21]. The equivalent loss resistance between the VSC and grid, and both equivalent inductance and resistance between the VSC and grid are estimated based on evaluation of closedloop transient responses of the current controller in [18] and [19], respectively.…”

“…In addition, only physical parameters can be estimated, whereas the controller parameters are still missing. Pseudorandom binary sequence is injected into current control loop of the VSCs, and the impedance information is obtained by performing the fast Fourier transform (FFT) on perturbed terminal voltage and output current, from which the parameters of L filter, transmission line impedance, and LCL filter are identified in [10], [13], and [14] respectively. The pseudorandom binary sequence-based parameter identification methods are relatively easy, since the perturbation signal is only composed of two electrical levels, i.e., +1 V and −1 V, which can be easily generated with a modest digital controller.…”

Adaptive controller based on grid impedance estimation for stable operation of grid‐connected inverters under weak grid conditions

“…Active methods generate disturbance signals at the point of common coupling (PCC) and observe the grid response to estimate grid impedance. The disturbance signal can be a transient current pulse [11–13], pseudorandom binary sequence (PRBS) current excitation [14, 15], current with a certain harmonic content [16, 17] or active and reactive power variations [18, 19]. These grid impedance estimation methods are summarised in Table 1.…”