Fanghong Guo

Distributed Secondary Voltage and Frequency Restoration Control of Droop-Controlled Inverter-Based Microgrids

In this paper, restorations for both voltage and frequency in the droop-controlled inverter-based islanded microgrid (MG) are addressed. A distributed finite-time control approach is used in the voltage restoration which enables the voltages at all the distributed generations (DGs) to converge to the reference value in finite time, and thus, the voltage and frequency control design can be separated. Then, a consensus-based distributed frequency control is proposed for frequency restoration, subject to certain control input constraints. Our control strategies are implemented on the local DGs, and thus, no central controller is required in contrast to existing control schemes proposed so far. By allowing these controllers to communicate with their neighboring controllers, the proposed control strategy can restore both voltage and frequency to their respective reference values while having accurate real power sharing, under a sufficient local stability condition established. An islanded MG test system consisting of four DGs is built in MATLAB to illustrate our design approach, and the results validate our proposed control strategy.

Distributed Economic Dispatch for Smart Grids With Random Wind Power

In this paper, we present a distributed economic dispatch (ED) strategy based on projected gradient and finite-time average consensus algorithms for smart grid systems. Both conventional thermal generators and wind turbines are taken into account in the ED model. By decomposing the centralized optimization into optimizations at local agents, a scheme is proposed for each agent to iteratively estimate a solution of the optimization problem in a distributed manner with limited communication among neighbors. It is theoretically shown that the estimated solutions of all the agents reach consensus of the optimal solution asymptomatically. This scheme also brings some advantages, such as plug-and-play property. Different from most existing distributed methods, the private confidential information, such as gradient or incremental cost of each generator, is not required for the information exchange, which makes more sense in real applications. Besides, the proposed method not only handles quadratic, but also nonquadratic convex cost functions with arbitrary initial values. Several case studies implemented on six-bus power system, as well as the IEEE 30-bus power system, are discussed and tested to validate the proposed method.

Distributed Cooperative Secondary Control for Voltage Unbalance Compensation in an Islanded Microgrid

This paper presents a distributed cooperative control scheme for voltage unbalance compensation (VUC) in an islanded microgrid (MG). By letting each distributed generator (DG) share the compensation effort cooperatively, unbalanced voltage in sensitive load bus (SLB) can be compensated. The concept of contribution level (CL) for compensation is first proposed for each local DG to indicate its compensation ability. A two-layer secondary compensation architecture consisting of a communication layer and a compensation layer is designed for each local DG. A totally distributed strategy involving information sharing and exchange is proposed, which is based on finite-time average consensus and newly developed graph discovery algorithm. This strategy does not require the whole system structure as a prior and can detect the structure automatically. The proposed scheme not only achieves similar VUC performance to the centralized one, but also brings some advantages, such as communication fault tolerance and plug-and-play property. Case studies including communication failure, CL variation, and DG plug-and-play are discussed and tested to validate the proposed method.

Design of open-loop controller for permanent magnet spherical motor

This paper presents an open-loop control system design for a permanent magnet spherical motor (PMSM). The proposed spherical motor consists of a ball-shaped rotor with a full circle of 8 permanent magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential 24 air-core coils. Based on the torque model of the PMSM, the relationship between current input and torque output can be demonstrated. We design the open-loop controller by decoupling the spinning motion control, which is based on the torque equilibrium theory, from the inclination motion control. Two types of spinning motion control models are proposed and analyzed. The open-loop controller can make the PMSM have the ability to spin continuously and tilt to certain angle. The experiment of open-loop control system based on a personal computer and current controller is designed to validate the control method at last.

Event-Based Consensus for Linear Multiagent Systems Without Continuous Communication

In this paper, we propose a new distributed event-trigger consensus protocol for linear multiagent systems with external disturbances. Two consensus problems are considered: one is a leader-follower case and the other is a nonleader case. Different from the existing results, our proposed scheme enables each agent to decide when to transmit its state signals to its neighbors such that continuous communication between neighboring agents is avoided. Clearly, this can largely decrease the communication burden of the whole communication network. Besides, since the control signal for each agent is discontinuous because of the event-triggering mechanism, the existence of a solution for the closed-loop system in the classical sense may not be guaranteed. To solve this problem, we employ a nonsmooth analysis technique including differential inclusion and Filippov solution. Through nonsmooth Lyapunov analysis, it is shown that uniformly bounded consensus results are derived and the bound of the consensus error is adjustable by choosing suitable design parameters.In this paper, we propose a new distributed event-trigger consensus protocol for linear multiagent systems with external disturbances. Two consensus problems are considered: one is a leader–follower case and the other is a nonleader case. Different from the existing results, our proposed scheme enables each agent to decide when to transmit its state signals to its neighbors such that continuous communication between neighboring agents is avoided. Clearly, this can largely decrease the communication burden of the whole communication network. Besides, since the control signal for each agent is discontinuous because of the event-triggering mechanism, the existence of a solution for the closed-loop system in the classical sense may not be guaranteed. To solve this problem, we employ a nonsmooth analysis technique including differential inclusion and Filippov solution. Through nonsmooth Lyapunov analysis, it is shown that uniformly bounded consensus results are derived and the bound of the consensus error is adjustable by choosing suitable design parameters.

A distributed hierarchical algorithm for multi-cluster constrained optimization

Abstract In this paper, we consider a constrained optimization problem for a large-scale multi-cluster agent system, in which a number of clusters already exist as a priori. The aim is to minimize a global objective function being the sum of multi-cluster local agents’ cost functions subject to certain global constraints. To solve this problem, a novel distributed hierarchical algorithm based on projected gradient method is proposed by using synchronous and sequential communication strategies. We firstly assign one agent as leader agent in each cluster, which can communicate with the leaders of its neighboring clusters. The agents in the same cluster conduct local optimization and communicate with their neighboring agents synchronously while the leader agents of different clusters exchange information in a sequential way. Then a scheme is proposed for each agent to iteratively estimate a solution of the optimization problem in a distributed manner. It is theoretically proved that the estimated solutions of all the agents reach consensus of the optimal solution asymptomatically when the chosen stepsizes are diminishing. Numerical examples are provided to validate the proposed method.

Distributed control subject to constraints on control inputs: A case study on secondary control of droop-controlled inverter-based microgrids

Through a case study in the secondary control of the droop-controlled inverter-based microgrid (MG), we illustrate the problem of distributed control subject to constraints on the control inputs. In order to eliminate the frequency deviation caused by the primary control while keeping the real and reactive power sharing property, the designed distributed controllers need to meet the requirement that the secondary frequency control inputs should be in proportion in the steady state. To address such a constraint, we propose a scheme to design distributed secondary controllers, which are implemented on the local distributed generations (DGs). By allowing these controllers to communicate with their neighboring controllers, the proposed control strategy can achieve satisfactory real and reactive power sharing accuracy while restoring the frequency to the nominal values. A tested MG system simulation validates our proposed control strategy.

Dynamic modelling and parameter identification of a three-degree-of-freedom spherical actuator

This paper addresses both dynamic modelling and dynamic parameter identification of a permanent magnet spherical actuator, which is capable of performing three-degree-of-freedom (DOF) motion in one single joint. The dynamic model of the spherical actuator is derived from Lagrange’s equations, but the parameters, called dynamic parameters, in the model are usually uncertain. Then the dynamic model is represented in a form that is linear in these parameters. A new identification method based on the output error (OE) method and recursive least square (LS) estimation is proposed to identify the parameters. This method only requires the current measurement of the stator coils in the identification procedure, which greatly simplifies the experimental process and improves the identification accuracy. Lastly, simulation and experimental results illustrate the effectiveness of the proposed method and its robustness to external disturbances. The proposed method can be also applied to other electromagnetic driving spherical actuators.

Distributed economic dispatch for a multi-area power system

In this paper, we present a distributed economic dispatch strategy for a multi-area power system. We treat each generator and load in the grid as an “agent”. Due to the large-scale number of the agents, the agents in the same area can be sorted as one group and each group has a leader to communicate with its neighboring areas. The agents in the same group can communicate synchronously while the leader agent of each group exchange information in a random sequential way. By decomposing the centralized optimization into optimizations at local agents, a scheme is proposed for each agent to iteratively estimate a solution of the optimization problem in a distributed manner. It is shown that the estimated solutions of all the agents reach consensus of the optimal solution asymptomatically. Different from most existing distributed methods, private confidential information such as gradient or incremental cost of each generator is not required for information exchange, which makes more sense in real applications. Besides, the proposed method not only handles quadratic but also non-quadratic convex cost functions with arbitrary initial values. A case study implemented on IEEE 30-bus power system are discussed and tested to validate the proposed method.

Bounded control of a spherical actuator based on orientation measurement feedback

This paper presents a permanent magnetic spherical actuator, which is capable of performing 3-degree-of-freedom (DOF). The orientation measurement of the spherical actuator has been a challenging problem so far. An interesting orientation measurement system for the rotor is proposed in this paper. Based on the position measurements, the trajectory tracking of the rotor with output feedback is addressed. As the current input is usually limited to certain degree in the applications, which leads to the bounded control torque input, the trajectory tracking controller with bounded torque input is designed. Simulation results indicate feasibility of the proposed controller. At last the experimental system is designed to validate the proposed orientation measurement system.