Method for Evaluation of the Utility’s and Consumers’ Contribution to the Current and Voltage Distortions at the PCC

In this article, a method that allows sharing responsibilities for the generation of harmonic currents between the utility and consumers powered by one point of common coupling (PCC) is addressed. For these purposes, mathematical modeling of the power supply system (PSS) with two consumers is carried out in order to introduce new indices using the simplest PSS structure as an example. Two indices are introduced that quantify the consumers’ contribution to the distortion of current and voltage at the PCC and that evaluate harmonic emission from the utility side. Experimental tests are carried out where both linear and nonlinear loads are considered, capacitive loads are taken into account, and harmonic distortions from the utility side are modeled to show the applicability of the indices in a wide range of load types. The experiments confirmed the theoretical results and illustrated that the quantitative assessment of the contributions is unambiguous. It suggests that the proposed criterion could be a reasonable basis for further tax policy on harmonic pollution for each consumer at the PCC and for the utility.

HESS in a Wind Turbine Generator: Assessment of Electric Performances at Point of Common Coupling with the Grid

Among Renewable Energy Sources (RES), wind energy is emerging as one of the largest installed renewable-power-generating capacities. The technological maturity of wind turbines, together with the large marine wind resource, is currently boosting the development of offshore wind turbines, which can reduce the visual and noise impacts and produce more power due to higher wind speeds. Nevertheless, the increasing penetration of wind energy, as well as other renewable sources, is still a great concern due to their fluctuating and intermittent behavior. Therefore, in order to cover the mismatch between power generation and load demand, the stochastic nature of renewables has to be mitigated. Among proposed solutions, the integration of energy storage systems in wind power plants is one of the most effective. In this paper, a Hybrid Energy Storage System (HESS) is integrated into an offshore wind turbine generator with the aim of demonstrating the benefits in terms of fluctuation reduction of the active power and voltage waveform frequency, specifically at the Point of Common Coupling (PCC). A MATLAB®/SimPowerSystems model composed of an offshore wind turbine interfaced with the grid through a full-scale back-to-back converter and a flywheel-battery-based HESS connected to the converter DC-link has been developed and compared with the case of storage absence. Simulations were carried out in reference to the wind turbine’s stress conditions and were selected—according to our previous work—in terms of the wind power step. Specifically, the main outcomes of this paper show that HESS integration allows for a reduction in the active power variation, when the wind power step is applied, to about 3% and 4.8%, respectively, for the simulated scenarios, in relation to more than 30% and 42% obtained for the no-storage case. Furthermore, HESS is able to reduce the transient time of the frequency of the three-phase voltage waveform at the PCC by more than 89% for both the investigated cases. Hence, this research demonstrates how HESS, coupled with renewable power plants, can strongly enhance grid safety and stability issues in order to meet the stringent requirements relating to the massive RES penetration expected in the coming years.

Fast harmonic analysis for PHIL experiments with decentralized real-time controllers

<i>The paper has been submitted to PSCC 2022 and is currently awaiting reviews.<br></i><br>This paper proposes and implements, a harmonic analysis algorithm for microgrid Power Hardware-in-the-loop (PHIL) experiments, when the point of common coupling (PCC) voltage cannot be directly wired to the local prosumer controllers due to long distances between them. Using frequency-shifting and filtering ideas, the voltage measurement is converted to magnitude and phase information. This is passed over an asynchronous communication link to another controller, where it is recovered into a waveform after delay compensation. The method allows for accurate power calculations and grid synchronization over distributed prosumer controllers. The proposed method can work at different execution rates depending on real time (RT) workload and is shown to be robust against step changes, harmonics and communication delays. The method is demonstrated with two PHIL experiments at the CoSES, TU Munich lab in grid connected and island mode.

Fast harmonic analysis for PHIL experiments with decentralized real-time controllers

<i>The paper has been submitted to PSCC 2022 and is currently awaiting reviews.<br></i><br>This paper proposes and implements, a harmonic analysis algorithm for microgrid Power Hardware-in-the-loop (PHIL) experiments, when the point of common coupling (PCC) voltage cannot be directly wired to the local prosumer controllers due to long distances between them. Using frequency-shifting and filtering ideas, the voltage measurement is converted to magnitude and phase information. This is passed over an asynchronous communication link to another controller, where it is recovered into a waveform after delay compensation. The method allows for accurate power calculations and grid synchronization over distributed prosumer controllers. The proposed method can work at different execution rates depending on real time (RT) workload and is shown to be robust against step changes, harmonics and communication delays. The method is demonstrated with two PHIL experiments at the CoSES, TU Munich lab in grid connected and island mode.

Microgrid modeling for contribution to the frequency control of power system

Recently, Distributed Energy Resources (DERs) are becoming more attractive to supply local loads under the concept of microgrids. These new parts of the power system have basically different dynamics compared with conventional power plants. Most of them are connected to the grid by power electronic interfaces, and their dynamic is determined by their controller. In this paper, the effect of the increased penetration of DERs on the load frequency problem of power systems is studied. The DERs of microgrids in each area are controlled to change their active power at Point of Common Coupling (PCC) after a disturbance in the power system. It is shown that with appropriate control of DERs in microgrids, the frequency deviation of the power system will decrease and the stability margin can be increased.

Enhancement of the Flickermeter for Grid-Connected Wind Turbines

Distributed generators connected to the power system usually produce voltage fluctuations. For wind turbines connected to a grid, large changes in wind speed can cause voltage flicker at the point of common coupling. The measurement of voltage flicker caused only by wind turbines is difficult. The wind turbine under test is usually connected to a medium voltage point, in which other fluctuating loads may produce significant voltage disturbances at the wind turbine terminal where the measurement is made. Although the IEC 61400-21-1 standard specifies a method to evaluate voltage flicker caused by wind turbines, because of the complex algorithm and process of the IEC standard, there is currently a lack of measurement equipment that meets the IEC standard. In addition, some countries that use other voltage flicker standards, such as ΔV10, do not have suitable flicker measurements for wind turbines. Therefore, this study proposes an enhanced version of the IEC 61400-21-1 standard, which integrates the ΔV10 method, so that the proposed measurement system complies with the IEC and ΔV10 standards. In this study, the voltage flicker measurement system is successfully implemented, which can help engineers to predict the voltage flicker by wind turbines and assess whether a region or grid is suitable for installing wind turbines. Therefore, it can provide wind turbine companies with a quick assessment of voltage flicker to comply with the certification process.