The utilization of power electronic inverters in power grids has increased tremendously, along with advancements in renewable energy sources. The usage of power electronic inverters results in the decoupling of sources from loads, leading to a decrease in the inertia of power systems. This decrease results in a high rate of change of frequency and frequency deviations under power imbalance that substantially affect the frequency stability of the system. This study focuses on the requirements of inertia and the corresponding issues that challenge the various country grid operators during the large-scale integration of renewable energy sources. This study reviews the various control techniques and technologies that offset a decrease in inertia and discusses the inertia emulation control techniques available for inverters, wind turbines, photovoltaic systems, and microgrid. This study attempts to explore future research directions and may assist researchers in choosing an appropriate topology, depending on requirements.

Future low-inertia power systems: Requirements, issues, and solutions - A review

DC microgrids encounter the challenges of constant power loads (CPLs) and pulsed power loads (PPLs), which impose the requirements of fast dynamics, large stability margin, high robustness that cannot be easily addressed by conventional linear control methods. This necessitates the implementation of advanced control technologies in order to significantly improve the robustness, dynamic performance, stability and flexibility of the system. This article presents an overview of advanced control technologies for bidirectional dc/dc converters in dc microgrids. First, the stability issue caused by CPLs and the power balance issue caused by PPLs are discussed, which motivate the utilization of advanced control technologies for addressing these issues. Next, typical advanced control technologies including model predictive control, backstepping control, sliding-mode control, passivity-based control, disturbance estimation techniques, intelligent control, and nonlinear modeling approaches are reviewed. Then the applications of advanced control technologies in bidirectional dc/dc converters are presented for the stabilization of CPLs and accommodation of PPLs. Finally, advanced control techniques are explored in other high-gain nonisolated (e.g., interleaved, multilevel, cascaded) and isolated converters (e.g., dual active bridge) for high-power applications.

Review on Advanced Control Technologies for Bidirectional DC/DC Converters in DC Microgrids

A virtual synchronous generator (VSG) control based on adaptive virtual inertia is proposed to improve dynamic frequency regulation of microgrid. When the system frequency deviates from the nominal steady-state value, the adaptive inertia control can exhibit a large inertia to slow the dynamic process and, thus, improve frequency nadir. And when the system frequency starts to return, a small inertia is shaped to accelerate system dynamics with a quick transient process. As a result, this flexible inertia property combines the merits of large inertia and small inertia, which contributes to the improvement of dynamic frequency response. The stability of the proposed algorithm is proved by Lyapunov stability theory, and the guidelines on the key control parameters are provided. Finally, both hardware-in-the-loop and experimental results demonstrate the effectiveness of the proposed control algorithm.

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Improvement of Frequency Regulation in VSG-Based AC Microgrid Via Adaptive Virtual Inertia

Microgrid control: A comprehensive survey

Due to the possibility of providing energy with much less dependence on the fossil fuels, renew-competent energy sources, in specified sun photovoltaic (PV) conversion have received elevated acceptance and progress in latest times. Big benefits of PV panels comprise easy and trustworthy power production and suitability for disbursed iteration. In addition the costs for photovoltaic modules is drastically lowering. To comprehend this issue, a control plan with modulation compensation scheme is likewise proposed. An exploratory three-stage seven-level cascaded H-bridge inverter has been manufactured using nine H-bridge modules (three modules for each stage). Each H-bridge module is associated with a 185-W solar panel. Simulation results are introduced to confirm the practicality of the proposed approach.

Modular Cascaded H-Bridge Multilevel PV Inverter with Distributed MPPT for Grid-Connected Applications

Direct current (dc) microgrids have been widely used in many critical applications. Such systems avoid unnecessary ac/dc conversions and can simplify control design. To achieve high-performance control of such system, advanced control algorithm needs to be designed. This paper presents a novel decentralized output constrained control algorithm for single-bus dc microgrids. The control objectives are to realize high-performance control of dc bus voltage, user-defined load sharing, and circulating current minimization. Unlike conventional control algorithms, the control algorithm can guarantee not only convergence but also bounded transient tracking error. By transforming the constrained system into an unconstrained system, the transient response of dc bus voltage can always stay within user-defined, time-varying bounds. Convergence of the transformed system can meet any transient performance requirement of the original system. Through proper control effort distribution, overall load demand can be shared among the distributed generators (DGs) according to predefined percentages. Accurate load sharing can indirectly minimize the harmful circulating currents among the DGs. Switch-level simulation and hardware experimentation with both single-bus and multiple-bus dc microgrids demonstrate the effectiveness of the proposed control design.

Decentralized High-Performance Control of DC Microgrids

The large inertia of a traditional power system slows down system U+02BC s frequency response but also allows decent time for controlling the system. Since an autonomous renewable microgrid usually has much smaller inertia, the control system must be very fast and accurate to fight against the small inertia and uncertainties. To reduce the demanding requirements on control, this paper proposes to increase the inertia of photovoltaic U+0028 PV U+0029 system through inertia emulation. The inertia emulation is realized by controlling the charging U+002F discharging of the direct current U+0028 DC U+0029-link capacitor over a certain range and adjusting the PV generation when it is feasible and U+002F or necessary. By well designing the inertia, the DC-link capacitor parameters and the control range, the negative impact of inertia emulation on energy efficiency can be reduced. The proposed algorithm can be integrated with distributed generation setting algorithms to improve dynamic performance and lower implementation requirements. Simulation studies demonstrate the effectiveness of the proposed solution.

Distributed virtual inertia based control of multiple photovoltaic systems in autonomous microgrid

To isolate the negative impacts of pulsed power loads (PPL) in a shipboard power system (SPS), energy storage systems (ESS) are usually equipped for online ESS charging and offline ESS discharging for PPL deployment. In order to achieve fast and smooth ESS charging, the generation control and ESS charging control need to be well coordinated. In addition, control constraints, such as generation and charging current bounds and ramp rates, and changes of operating conditions during charging, should also be properly considered. To better solve this important but insufficiently investigated problem, two control algorithms are presented in this paper. The first PI-based control algorithm is designed based on analysis of the desired performance and rules for coordination. The second feedback linearization based control algorithm is designed based on a simplified SPS model and ramp rates difference of supply and demand. The algorithms are simple to implement and can effectively reduce the negative impacts during supercapacitor charging. The algorithms are tested with detailed single-generator and multiple-generator SPS models. Power hardware-in-the-loop and real-time digital simulation studies are performed to demonstrate the effectiveness of the proposed algorithms.

Cooperative Controls for Pulsed Power Load Accommodation in a Shipboard Power System

Conventional control solutions of the inverter-interfaced microgrids are usually designed based on models with fully decoupled subsystems. The negligence of the strong coupling due to power lines impedance leads to large transient line currents, which might trigger false protection. Besides, the droop-based control methods unnecessarily introduce system frequency and voltage deviations. To overcome these issues, a novel distributed control scheme is proposed for the inverter-interfaced microgrids in this paper. The objective of the primary control is to regulate the bus voltages and frequency while suppressing the transient line currents. The objective of secondary control is to maintain fair load sharing. Both primary control and secondary control are distributed and subsystems or control agents only require measurements from local and neighboring subsystems. The detailed control problem formulation, control design, and stability analysis are presented in this paper. The effectiveness of the proposed control solution is evaluated through extensive simulations based on both simplified and detailed models.

Distributed Control of Inverter-Interfaced Microgrids Based on Consensus Algorithm With Improved Transient Performance

Pulsed power load (PPL) consumes a huge amount of energy within a very short period of time. Directly connecting a PPL to a shipboard power system (SPS) will cause large disturbance even instability during PPL deployment. As an important category of energy storage system (ESS), the flywheel ESS (FESS) is an ideal source for PPL accommodation. By powering the PPL separately with a sufficiently charged FESS, the negative impacts of PPL on SPS can be avoided. The paper presents an adaptive output-constrained control design that can realize fast charging of the FESS and simultaneously minimize the disturbance to system frequency. Major benefit of the algorithm is that transient response can be guaranteed to stay within user-defined, time-varying bounds. This property makes the algorithm different from typical adaptive control algorithms and very appealing for high-performance applications. By applying the standard Lyapunov synthesis, all closed-loop signals are proved to be bounded. Finally, the proposed control design is tested through simulations using SPS models with different details. Simulation results demonstrate the effectiveness of the proposed control design.

Cheng Wang

Papers

Decentralized High-Performance Control of DC Microgrids

Distributed virtual inertia based control of multiple photovoltaic systems in autonomous microgrid

Cooperative Controls for Pulsed Power Load Accommodation in a Shipboard Power System

Distributed Control of Inverter-Interfaced Microgrids Based on Consensus Algorithm With Improved Transient Performance

Performance Guaranteed Control of Flywheel Energy Storage System for Pulsed Power Load Accommodation