For Fault Ride Through Research Articles

Enabling LVRT Compliance of Electrolyzer Systems Using Energy Storage Technologies

This paper presents a comprehensive techno-economic analysis of different energy storage systems (ESSs) in providing low-voltage ride-through (LVRT) support for power electronics-based electrolyzer systems. A framework for analyzing the performance of a grid-integrated electrolyzer-ESS system is developed, taking into account realistic scenarios and accurate models. The system components consist of a 500 kW alkaline electrolyzer module integrated with a medium-voltage grid and three different commercially available ESSs based on Li-ion battery, Li-ion capacitor, and supercapacitor technology, respectively. The performance of these ESSs is extensively studied for three LVRT profiles, with a primary focus on the upcoming Danish grid code. In order to perform simulation studies, the system is implemented on the MATLAB®/Simulink®-PLECS® platform. The results demonstrate that all three energy storage technologies are capable of supporting the electrolyzer systems during low-voltage abnormalities in the distribution grid. The study also reveals that the supercapacitor-based technology seems to be more appropriate, from a techno-economic perspective, for fault ride-through (FRT) compliance.

Fault ride-through capability improvement in a DFIG-based wind turbine using modified ADRC

In this paper, an overview of several strategies for fault ride-through (FRT) capability improvement of a doubly-fed induction generator (DFIG)-based wind turbine is presented. Uncertainties and parameter variations have adverse effects on the performance of these strategies. It is desirable to use a control method that is robust to such disturbances. Auto disturbance rejection control (ADRC) is one of the most common methods for eliminating the effects of disturbances. To improve the performance of the conventional ADRC, a modified ADRC is introduced that is more robust to disturbances and offers better responses. The non-derivability of the fal function used in the conventional ADRC degrades its efficiency, so the modified ADRC uses alternative functions that are derivable at all points, i.e., the odd trigonometric and hyperbolic functions (arcsinh, arctan, and tanh). To improve the efficiency of the proposed ADRC, fuzzy logic and fractional-order functions are used simultaneously. In fuzzy fractional-order ADRC (FFOADRC), all disturbances are evaluated using a nonlinear fractional-order extended state observer (NFESO). The performance of the suggested structure is investigated in MATLAB/Simulink. The simulation results show that during disturbances such as network voltage sag/swell, using the modified ADRCs leads to smaller fluctuations in stator flux amplitude and DC-link voltage, lower variations in DFIG velocity, and lower total harmonic distortion (THD) of the stator current. This demonstrates the superiority over conventional ADRC and a proportional-integral (PI) controller. Also, by changing the crowbar resistance and using the modified ADRCs, the peak values of the waveforms (torque and currents) can be controlled at the moment of fault occurrence with no significant distortion.

A Single-Ended Fault Location Method for Grid-Connected Converter System Based on Control and Protection Coordination

Traditional single-ended fault location method is influenced by the fault resistance, and the remote in feed, which reflects as the two equations built by fault phase have four unknowns. And in the grid-connected converter system, the weak feedback characteristic further reduces the performance of the method. To solve it, a single-ended fault location method based on control and protection coordination is proposed in this paper. First, using the high controlled-ability of the converter, the control strategy for fault ride-through (FRT) operation is divided into two stages by switching control modes. Then, according to the electrical quantities under two stages, four uncorrelated equations can be established, and the equations still have four unknown parameters. The fault distance can be calculated by solving them. The simulation results show that the proposed method has high accuracy and is immune to fault resistance and fault location, it solves the problem of insufficient equations in principle.

Enhancement of fault ride-through capability of grid-connected wind farm

The distributed power generation (DPG) at low and medium voltage demands that the renewable generation system is always grid connected during fault condition to ensure the stability of wind power system. The DPG consist of wind turbines (WT) along with fixed speed induction generator (FSIG) does not provide accurate reactive power control and hence, there is need for dedicated compensation. Due to fault condition, the negative sequence component is affected and there is direct impact on DPG with reduction in life expectancy. This paper proposes the application of distributed static compensator (DSTATCOM) for fault ride through (FRT) and reactive power compensation. It has been observed that the compensation of negative sequence component improves the performance of FSIG-based WT. Also, the compensation of positive sequence component avoids the collapsing of voltage and improved the stability of WT. The simulation is done in MATLAB and various tests are considered under fault condition in which results are presented. The FRT enhancement of grid connected WT by using DSTATCOM is 30% and hence, 30% additional wind power is penetrated to the grid.

Combinational voltage booster technique for fault ride-through capability enhancement of squirrel-cage induction generator

This paper proposes a combinational voltage booster technique for fault ride-through (FRT) capability enhancement of squirrel-cage induction generators (SCIGs) by a multifunctional series compensator (MFSC). This technique uses a couple of antiparallel thyristors across the ac terminals of a traditional dynamic voltage restorer (DVR). Two control schemes are applied: a DVR mode and a multifunctional mode. The MFSC can operate in the DVR mode to compensate the slight voltage fluctuations/imbalances at the point of common coupling (PCC). Also, when serious voltage sags occur in the line, the MFSC controller deactivates the faulty phase inverter and activates its corresponding thyristors to insert the equivalent impedance to maintain the voltage level during the fault. Then, it switches to DVR mode to improve the recovery time after the fault. An operational algorithm is applied to deal with different voltage sag depths caused by various fault conditions (both symmetrical and asymmetrical faults). Comprehensive simulations were carried out by using PSCAD/EMTDC software, and results show that the proposed technology is a very effective device to improve the FRT capability of the SCIG. A scaled-down experimental verification was carried out. Experimental results confirm the effectiveness of the combinational voltage booster technique of the MFSC for both slight and serious voltage sags.

Performance Analysis of a Sliding Mode Control for Distributed Generations

This paper presents the performance of a sliding mode based hybrid controller for three phase voltage source inverter. The main objective of this analysis is to observe the effectiveness of the controller for fault ride through (FRT) capability improvement of the DC based distributed generations (DG). The performance of the conventional PI based cascaded controller is also presented for comparison purpose.

モデル追従制御インバータによる風力発電系統連系の位相特性

Wind energy is a clean and renewable energy source. A wind generator using a PMSG can operate in maximum power point tracking (MPPT) mode. In addition, it has capabilities for fault ride through (FRT), active power and reactive power control issues, and voltage regulations. We have already proposed a model following controlled PWM inverter that exhibits robustness. The proposed inverter can output a sine wave current regardless of the rippling input voltage. This paper presents a numerical simulation analysis of the transient characteristics of the discrete-time model following controlled PWM inverter for a wind turbine generator system with a synchronized grid interface.