Dazhong Ma

A Novel Energy Function-Based Stability Evaluation and Nonlinear Control Approach for Energy Internet

Unlike conventional interconnected power systems, energy Internet presents an unsolved and more challenging problem for the society including transfer impedance, damping, large penetration of distributed generation, and numerous hybrid integration of generators and converters. In this paper, a novel energy function designed for energy internet router is proposed to accurately evaluate its transfer stability. The reliability of the proposed energy function is confirmed through both theoretical analysis and empirical simulations. Furthermore, generalized methods to determine critical stable energy, stable domain, and critical clearing time are proposed. By updating stability criterion and evaluating system energy of post-disturbance system, fault energy-based impulsive feedback control method is specifically designed for energy Internet to stabilize the system. Simulation and experimental results are provided to validate the effectiveness of the proposed energy function and nonlinear control method.

Data-Driven Control for Interlinked AC/DC Microgrids Via Model-Free Adaptive Control and Dual-Droop Control

This paper investigates the coordinated power sharing issues of interlinked ac/dc microgrids. An appropriate control strategy is developed to control the interlinking converter (IC) to realize proportional power sharing between ac and dc microgrids. The proposed strategy mainly includes two parts: 1) the primary outer-loop dual-droop control method along with secondary control; and 2) the inner-loop data-driven model-free adaptive voltage control. Using the proposed scheme, the IC, just like the hierarchical controlled distributed generator units, will have the ability to regulate and restore the dc terminal voltage and ac frequency. Moreover, the design of the controller is only based on input/output measurement data, but not the model any more, and the system stability can be guaranteed by the Lyapunov method. The detailed system architecture and proposed control strategies are presented in this paper. Simulation and experimental results are given to verify the proposed power sharing strategy.

Optimal Placement of Energy Storage Devices in Microgrids via Structure Preserving Energy Function

As system transient stability is one of the most important criterions of microgrid (MG) security operation, and the performance of an MG strongly depends on the placement of its energy storage devices (ESDs); optimal placement of ESDs for improving system transient stability is required for MGs. An MG structure preserving energy function is first developed for voltage source inverter-based MGs since the existing energy functions, based on synchronous generators and the conventional power system, are not applicable for MGs. The concept of internal potential energy of distributed energy resource is presented instead of the kinetic energy term in traditional energy function. Then, a novel approach for the optimal placement of ESDs is proposed based on MG structure preserving energy function for improving MG transient stability. Simulation and experimental results show that the proposed method can be used to find the optimal placement of ESDs and improve the system stability effectively.

Quasi-Z-Source Network-Based Hybrid Power Supply System for Aluminum Electrolysis Industry

A hybrid power supply system (HPSS) based on the quasi-Z-source network is proposed for aluminum electrolysis, which can reduce energy consuming and carbon emission through the use of renewable energy. An ac–dc integrate controller is designed in the HPSS that contains a two-layer control. The first layer control is responsible for maintaining the dc bus voltage and current, which can mitigate negative effects caused by anode effect in aluminum electrolysis. The independent maximum power tracking for PV array and the dc-bus voltage balance for each quasi-Z-source dc–dc converter can be achieved by using the PV-voltage controller and dc-bus voltage controller for the PV System. To maintain the voltage of dc bus within the require voltage range of aluminum electrolysis production and ensure high input power quality of ac System, the quasi-Z-rectifier controller is employed, which can reduce the harmonic injection. The power allocation is addressed in the second control layer and a power scheme algorithm (PSA) is carried out to maximize the system efficiency and economic benefit. At last, the simulation and experimental results are provided to verify the effectiveness of the designed HPSS and the proposed PSA.

A disaster-triggered life-support load restoration framework based on Multi-Agent Consensus System

To guarantee the life-support line unblocked under extreme disasters, a life-support load emergency restoration problem is studied. A life-support load restoration framework is proposed for an efficient restoration, which consists of a hybrid triggering mechanism and a Multi-Agent Consensus System (MACS). The hybrid triggering mechanism is proposed to identify life-support loads rapidly, as a disaster-caused blackout occurs. Meanwhile, communication network bandwidth is saved greatly. The novel MACS is developed as a restoration operator. Multi-agent consensus algorithm, as an Action Consensus Protocol of Agents (ACPA), is firstly applied in power systems restoration. Based on the proposed ACPA, the emergency restoration can be quantized precisely. Simulation results on IEEE-30 bus system are provided to validate the performance of the proposed approach.

Fault tolerant synchronization of chaotic systems with time delay based on the double event-triggered sampled control

This paper is concerned with the fault tolerant synchronization of the master-slave chaotic system. Based on the double event-triggered scheme, the sampled controller, which yellow includes the fault compensator and state feedback controller, is designed to achieve the fault tolerant synchronization. When the fault exceeds the threshold value, the fault compensator can eliminate its effect in synchronized chaotic system. The double event-triggered scheme is composed of the system trigger and fault trigger, which can judge whether or not the newly sampled signal should be transmitted to the fault compensator and state feedback controller. It can make more appropriate use of network resources and increase the robustness of synchronized chaotic system. Based on the input delay method, the solution of the controller is converted to guarantee the stability of chaotic errors system. By constructing the Lyapunov–Krasovskii functional and employing the Wirtingerbrk inequality, sufficient conditions for asymptotical stability of the chaotic error system are derived for achieving the fault tolerant synchronization through linear matrix inequality approach. Finally, a numerical simulation example is discussed to prove the practical utility of this method.

A Hierarchical Cluster Synchronization Framework of Energy Internet

The concept of “Energy Internet” has been recently proposed to improve the efficiency of renewable energy resources. Accordingly, this paper investigates the synchronization of the Energy Internet system. Specifically, an appropriate hierarchical cluster synchronization framework is firstly developed for the Energy Internet, which includes primary synchronization, secondary synchronization, and tertiary synchronization. Furthermore, a secondary synchronization strategy (cluster synchronization) is proposed for the synchronization of multiple microgrid clusters in the Energy Internet, which is based on the consensus algorithm of multiagent networks. The detailed synchronization framework and control scheme are presented in this paper. Finally, some simulation results are provided and discussed to validate the performance and effectiveness of the proposed strategy.

The initial guess estimation newton method for power flow in distribution systems

With the increasing integration of distributed generations U+0028 DGs U+0029, there is a demand for DGs to play a more important role on the voltage regulation. Meanwhile, the high penetration of DGs could raise a technical problem that the distribution system may operate with bi-directional power flow, leading to the inadequacy of the traditional power flow. Considering this new scenario in distribution system power flow, the convergence theorem is proposed, which contributes to develop a novel selection method of the initial guess closed to the convergent solution. Moreover, to ensure the fast rate of power flow convergence, the theorem of the maximum iterations estimation is also proposed. Based on the two proposed theorems, an Initial Guess Estimation Newton method is proposed, considering different operational status of DGs and initial guess sensitivity simultaneously. Based on the standard node systems, Tongliao grid, and 69 system of USA, three simulation examples are provided to illustrate the effectiveness of the proposed method.

Event-Based Distributed Active Power Sharing Control for Interconnected AC and DC Microgrids

This paper investigates the issue of active power sharing among a cluster of microgrids formed by a set of ac and dc microgrids network-interconnected through a set of interlinking converters (ICs). An event-based distributed consensus control approach is proposed to address this issue, in which each IC is assigned to be an agent that needs only the information of its local and neighboring ICs. We first construct the agent system for each IC and design its consensus control protocol. This control mechanism uses a cooperative approach to indirectly adjust the active power load of individual microgrid and, accordingly, navigate the active power flow among them. Thus active power sharing among the interconnected microgrids can be achieved proportionally. Then, an event-based control scheme is utilized to design the consensus protocol, which can dramatically reduce the communication between ICs. Communication time delays and reactive power support are also considered. The proposed distributed control method allows a sparse communication structure and higher reliability and flexibility operation. Simulation results are presented to demonstrate the proposed control method.

Modeling Single-Phase Inverter and Its Decentralized Coordinated Control by Using Feedback Linearization

It is a very crucial problem to make a microgrid operated reasonably and stably. Considering the nonlinear mathematics model of inverter established in this paper, the input-output feedback linearization method is used to transform the nonlinear mathematics model of inverters to a linear tracking synchronization and consensus regulation control problem. Based on the linear mathematics model and multiagent consensus algorithm, a decentralized coordinated controller is proposed to make amplitudes and angles of voltages from inverters be consensus and active and reactive power shared in the desired ratio. The proposed control is totally distributed because each inverter only requires local and one neighbor’s information with sparse communication structure based on multiagent system. The hybrid consensus algorithm is used to keep the amplitude of the output voltages following the leader and the angles of output voltage as consensus. Then the microgrid can be operated more efficiently and the circulating current between DGs can be effectively suppressed. The effectiveness of the proposed method is proved through simulation results of a typical microgrid system.