Low voltage ride-through capability improvement of microgrid using a hybrid coordination control strategy

Abstract

This paper proposes a hybrid coordination control strategy to improve the low voltage ride-through (LVRT) capability of microgrids. During microgrid external failure, the overcurrent and the voltage sag of the microgrid can be effectively suppressed. Compared with traditional control strategies, the microgrid transient performance can also be enhanced by adopting a generalized control algorithm, performing the active switching of the energy storage (ES) operation mode and triggering the inductance-type flux coupling fault current limiters (FCLs). Among them, according to the hierarchical control structure of the grid-connected inverter, the generalized control algorithm is applied to ES. Through the two degrees of freedom's control principle and inverse plant modeling techniques, the generalized control algorithm can make the control layer of the ES inverter operate in all control targets (i.e., PQ control, droop control and Vf control), with a single control structure. Also, it eliminates the effects of microgrid distortion voltage and ES surge current on the control system of the ES inverter. For the inverter application layer, by introducing microgrid voltage and angular frequency feedforward compensation, the voltage and frequency fluctuation of the microgrid can be suppressed efficiently under the fault conditions. Therefore, with the help of the generalized control algorithm, the active switching function of ES can be carried out successfully, which is the key technology for microgrids to realize their operational mode smooth switching. Meanwhile, the voltage sag and overcurrent of microgrids can be significantly mitigated through generating reactive power from microgrids and injecting it into inductance-type FCLs with lower cost. The related theoretical derivation and simulation analysis under various scenarios (including asymmetric faults) confirm that the proposed control strategy can not only enhance the LVRT capability, but also strengthen the microgrid transient performance.

A Comprehensive Review on Power-Quality Issues, Optimization Techniques, and Control Strategies of Microgrid Based on Renewable Energy Sources

“…Many standards and grid codes impose new regulations about the integration of RES against voltage swells and the ability to withstand voltage sags (Low-Voltage Ride Through (LVRT)) and voltage swells (High-Voltage Ride Through (HVRT)). These regulations require that the HMGs be disconnected from the utility grid in case the voltage sags or swells last for a certain duration [67]. To cite an example, the German standard indicates that in the presence of voltage sags (below their nominal value), the HMGs must remain connected to the utility grid for 0.15 s; otherwise, system shutdown will be mandatory.…”

Electric Power Conversion and Micro-Grids

“…As the integration of DES in microgrids increases, many standards and grid codes impose new regulations, such as the ability to withstand voltage sags (LVRT) and voltage swell (HVRT). These regulations require that the microgrids disconnect from the grids in case the voltage sags or swell has a specific duration [115]. In the case of voltage sags, the German standard dictates that the microgrids must remain connected and withstand the event by providing reactive power even if the voltage sags to 0% of its nominal value for 0.15 s; otherwise, disconnection is mandatory.…”

Power Quality in Microgrids Including Supraharmonics: Issues, Standards, and Mitigations

“…As the integration of DES and MG increases, many standards and GCs are imposing new regulations, such as low-voltage ride-through (LVRT) and high-voltage ride-through (HVRT) in case of sag and swell, respectively. Such regulations require the MG sources to disconnect from the grid in case the sag or swell lasts for a specified time [71].…”