Qiuye Sun

A Multiagent-Based Consensus Algorithm for Distributed Coordinated Control of Distributed Generators in the Energy Internet

With the bidirectional power flow provided by the Energy Internet, various methods are promoted to improve and increase the energy utilization between Energy Internet and main grid (MG). This paper proposes a novel distributed coordinated controller combined with a multiagent-based consensus algorithm, which is applied to distributed generators in the Energy Internet. Then, the decomposed tasks, models, and information flow of the proposed method are analyzed. The proposed coordinated controller installed between the Energy Internet and MG keeps voltage angles and amplitudes consensus, while providing accurate power-sharing and minimizing circulating currents. Finally, the Energy Internet can be integrated into the MG seamlessly if necessary. Hence, the Energy Internet can be operated as a spinning reserve system. Simulation results are provided to show the effectiveness of the proposed controller in an Energy Internet.

Hybrid Three-Phase/Single-Phase Microgrid Architecture With Power Management Capabilities

With the fast proliferation of single-phase distributed generation (DG) units and loads integrated into residential microgrids, independent power sharing per phase and full use of the energy generated by DGs have become crucial. To address these issues, this paper proposes a hybrid microgrid architecture and its power management strategy. In this microgrid structure, a power sharing unit (PSU), composed of three single-phase back-to-back (SPBTB) converters, is proposed to be installed at the point of common coupling. The aim of the PSU is mainly to realize the power exchange and coordinated control of load power sharing among phases, as well as to allow full utilization of the energy generated by DGs. Meanwhile, the method combining the modified adaptive backstepping-sliding mode control approach and droop control is also proposed to design the SPBTB system controllers. With the application of the proposed PSU and its power management strategy, the loads among different phases can be properly supplied and the energy can be fully utilized, as well as obtaining better load sharing. Simulation and experimental results are provided to demonstrate the validity of the proposed hybrid microgrid structure and control.

Distributed Adaptive Virtual Impedance Control for Accurate Reactive Power Sharing Based on Consensus Control in Microgrids

To achieve accurate reactive power sharing regardless of the effects of mismatched line impedance, this paper proposes a reactive power sharing method that employs both consensus control and adaptive virtual impedance control for islanded microgrids. The consensus control is used to find the reactive power mismatch among distributed generation (DG) units. The reactive power mismatch term is fed to a proportional integral controller to generate the virtual impedance correction. With fully distributed regulation of the DG virtual impedance, the load reactive power will be shared accurately among DGs and the circulating line currents among DGs are effectively suppressed. The control strategy does not require the knowledge of the line impedances. Also, the average voltage restoration based on a dynamic consensus control is proposed to recover the decreased output voltage of each DG due to the droop action and the added virtual impedance. Simulation results show the effectiveness of the proposed method in achieving load reactive power sharing and the voltage restoration.

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.

Adaptive critic design-based robust neural network control for nonlinear distributed parameter systems with unknown dynamics

Abstract In this paper, an adaptive critic design (ACD)-based robust on-line neural network control design is developed for a class of parabolic partial differential equation (PDE) systems with unknown nonlinear dynamics. First, the Galerkin method is applied to the parabolic PDE system to derive a finite-dimensional slow one and an infinite-dimensional stable fast subsystem. The obtained slow system is an ordinary differential equation (ODE) system with unknown nonlinearities, which accurately describes the dynamics of the slow modes of the PDE system. Then, a novel ACD-based robust optimal control scheme is proposed for the resulting nonlinear slow system with unknown dynamics. An action neural network (NN) is employed to approximate all the derived unknown nonlinear terms and a robust control term is further developed to attenuate the NN reconstruction errors and disturbances. Especially, by developing novel critic signals and Lyapunov function candidate, together with the adaptive bounding technique, no a prior knowledge for the bounds of the disturbance term, the NN ideal weights of action NN and critic NN and the NN reconstruction errors is required. Finally, simulation results demonstrate the effectiveness of the proposed robust optimal control scheme.

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.

Consensus-Based Distributed Control for Accurate Reactive, Harmonic, and Imbalance Power Sharing in Microgrids

This paper investigates the issue of accurate reactive, harmonic, and imbalance power sharing in a microgrid. Harmonic and imbalance droop controllers are developed to proportionally share the harmonic power and the imbalance power among distributed generation (DG) units and improve the voltage quality at the point of common coupling (PCC). Further, a distributed consensus protocol is developed to adaptively regulate the virtual impedance at fundamental frequency and selected harmonic frequencies. Additionally, a dynamic consensus based method is adopted to restore the voltage to their average voltage. With the proposed methods, the microgrid system reliability and flexibility can be enhanced and the knowledge of the line impedance is not required. And the reactive, harmonic, and imbalance power can be proportionally shared among the DG units. Moreover, the quality of the voltage at PCC can be greatly improved. Simulation and experimental results are presented to demonstrate the proposed method.

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.

Distributed optimal co-multi-microgrids energy management for energy internet

Unlike conventional power systems, the upcoming energy internet (EI) emphasizes comprehensive utilization of energy in the whole power system by coordinating multi-microgrids, which also brings new challenge for the energy management. To address this issue, this paper proposes a novel consensus-based distributed approach based on multi-agent framework to solve the energy management problem of the energy internet, which only requires local information exchange among neighboring agents. Correspondingly, two consensus algorithms are presented, one of which drives the incremental cost of each distributed generator (DG) converge to the state of the leader agent-energy router, and the other one is used to estimate the global power mismatch, which is a first-order average consensus algorithm modified by a correction term. In addition, in order to meet the supply-demand balance, an effective control strategy for the energy router is proposed to accurately calculate the power exchange between the microgrid and the main grid. Finally, simulation results within a 7-bus test system are provided to illustrate the effectiveness of the proposed approach.

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.