To study unplanned islanding transient response of microgrid by implementing MSOG and SRF‐PLL based hierarchical control in the presence of non‐linear loads

Abstract

This study considers the hierarchical control of microgrid and harmonic compensation of non-linear load specially in transition from grid-connected to unplanned islanding. The proposed controllers are based on the stationary reference frame with hierarchical control levels (inner, primary, and secondary). In the inner control loop, proportional and multi-resonant voltage and current controllers for three-phase voltage source inverters are proposed. Moreover, a droop control is used to share active and reactive power in the primary control loop. To achieve decoupled active and reactive power sharing, virtual impedance loop is implemented, too. The mentioned procedure increases the total impedance and consequently reduces the initial current and subsequently facilitates the continuous connection of DGs to the MG. To attain smoother transition, selective harmonic virtual impedance is applied by multiple second-order generalised integrator module to extract the fundamental positive sequence and harmonic components of the output current of the DGs. In secondary control level, synchronisation procedure is considered to make connection and restoration by the advanced three-phase synchronous reference frame PLL with in-loop moving average filter which significantly enhances its disturbance rejection capability. The results are shown smoother transition, robustness, and high performance of the proposed hierarchical control VSIs during variation of system configuration.

An Improved Hierarchical Control Structure for Robust Microgrid Operation and Seamless Mode Transfer under Linear and Nonlinear Loads conditions

“…As referred to literature [1,8,9], according to ANSI/ISA-95 standard, the structure of MGs hierarchical control can be arranged into four levels: the inner level with two control loops which consists of voltage and current controllers, the primary level that can contain virtual impedance and droop control, the secondary level which comprises restoration and synchronization loops, and finally territory level that includes economically optimal operation, power management, and power market. Here, the concentration of the hierarchical-based structure of the proposed scheme is on the inner, primary, and secondary levels.…”

“…Therefore, the HCS is proposed to enhance efficiency, reliability, control capability, and operation cost. Also, it can use different resources based on different capacities, topologies, and technologies organized in MG [7][8][9].…”

“…The other reason for MG and power system transitions is load type. There are different load types in power system such as linear [10][11][12][13], nonlinear [2,8,9], balanced [2,11], unbalanced [3,14] loads. Two adaptive and smart controllers are planned to regulate the MG frequency and voltage accurately in IM [10].…”

“…Consequently, many advanced SRF-PLLs with high competence to reject the disturbance are introduced which contain different in loop filters and prefilter [16][17][18][19]. Here, the synchronous reference frame phase locked-loop with inloop MAF designed in the last study [8] is applied which has high efficiency in harmonic distortion.…”

Guest Editorial: Challenges in Future Grid‐Interactive Power Converters: ControlStrategies, Optimal Operation, and Corrective Actions

“…Paper [19] proposes dual‐stage cascaded control to resynchronize an isolated microgrid with the utility. Paper [20] designs a hierarchical control for microgrids to transit from grid‐connected to unplanned islanding in the presence of linear and nonlinear loads.…”