Test methodology for validation of multi‐frequency models of renewable energy generators using small‐signal perturbations

Abstract

Providing trustworthy and accurate multi-frequency (or harmonic) models for renewable energy generators (REG) is an ongoing challenge for harmonic studies. There have been effective attempts to propose and design a test device to validate the harmonic models, mainly based on shunt current perturbations. However, using additional devices for perturbations is costly for converter-based test sites. This paper provides the test specifications to extend the application of the grid emulators for voltage perturbations and appropriate harmonic model validation. Besides, the effects of the sequence couplings, initial emissions, and power set-points on the test results have been overlooked in the literature. Considering these effects, this paper proposes a generic test methodology to obtain more accurate models in the sequence domain. The experimental verification of the proposed methodology is demonstrated using a 7 MVA grid emulator for testing of a 2 MVA photo-voltaic converter and a 2 MVA Type 3 wind turbine. This way, the test challenges, specifications, and recommendations are presented using the MW-scale experiments on different REGs. Furthermore, the effects of sequence couplings and initial emissions on the calculation results are investigated and compared. The proposed methodology is applicable for harmonic model validation as well as empirical modelling.

Generic Multi-Frequency Modelling of Converter-Connected Renewable Energy Generators Considering Frequency and Sequence Couplings

“…The experimental single-tone voltage perturbation tests are performed by a 7MVA/ 13.8kV grid emulator at National Renewable Energy Laboratory (NREL), USA [11], [21], [40]. We have illustrated the simulation results of perturbation tests on Type 4 and Type 3 WTs in reference [41].…”

“…In this paper, the experimental perturbation tests are performed on a balanced three-phase 2MVA PV converter with the fundamental frequency of 60Hz. The three-phase voltage and currents are measured using data acquisition modules with 50kS/s speed and 18bit resolution [11], [21]. According to the proposed methodology in Fig.…”

Application of a Novel Synergetic Control for Optimal Power Extraction of a Small-Scale Wind Generation System with Variable Loads and Wind Speeds

“…The setup consisted of a WT emulator, which can accurately reproduce the mechanical behavior of a real WT. A detailed description of this emulator is found in [38,39]. The controls and the MPPT were instigated on a dSPACE 1104 card and programmed using MATLAB/Simulink, as depicted in Figure 10, to validate the proposed control strategy.…”

Extension of the Generic Multi-Frequency Modelling Method for Type 3 Wind Turbines

“…2. Accordingly, the parameters of the generic model can be derived using single-tone positive and negative sequence perturbations as explained in [14]- [15]. In the next step, the Discrete Fourier Transform (DFT) of the WT response against perturbations are calculated and transformed to the sequence domain.…”

“…The positive sequence currents and voltages are derived from positive sequence perturbations at "f i + f 0 " and the negative sequence components are calculated from negative sequence perturbations at "f i − f 0 " [9]- [10], [14]. Besides, in [15], a test 0885-8969 (c) 2021 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.…”