The Internet of Things (IoT) has led the way to smarter and ultimately more efficient cyberphysical systems (CPSs). An example of such a CPS includes motor drives connected to a computer network controlling industrial processes. Another example is a recent European Union regulation that may enable utility customers to become energy suppliers-i.e., the formation of transactive energy (TE) systems or energy local area networks (E-LANs) formed by integrated smart energy nodes cooperating to accomplish system goals.

Cybersecurity and Power Electronics: Addressing the Security Vulnerabilities of the Internet of Things

Traditional droop control strategy has lack of the decoupling ability, so the efficiency and stability of the microgrid based on the traditional droop control strategy are easily affected by the uncontrollable coupling of the distributed generation (DG) units. In this paper, an improved droop control strategy incorporating the coupling compensation and virtual impedance is proposed to improve the efficiency and stability of the microgrid. Its coupling compensation comprises the angular frequency deviation compensation and voltage deviation compensation, which decreases the influence of the uncontrollable coupling. The virtual impedance can change the characteristics of the line impedance of the DG units and reduce their coupling. Therefore, the combination of the coupling compensation and virtual impedance can greatly reduce the power circulating-current of the microgrid and improve its dynamic performance. Then, an improved particle swarm optimization algorithm incorporating the multi-swarm and multi-velocity is taken to optimize the parameters of the coupling compensation with high accuracy and high reliability. Simulation and experimental results validate the high performance of the improved droop control strategy.

Droop Control Strategy Incorporating Coupling Compensation and Virtual Impedance for Microgrid Application

In DC microgrids, the inherent inertia from DC capacitors is low and the DC bus voltage is susceptible to power fluctuations, which results in low DC voltage quality. In this article, an inertia and damping control (IDC) method is proposed and applied in the energy storage system to strengthen the inertia and damping of DC microgrids. The proposed control strategy is obtained based on the charging and discharging conversion form of capacitors and aims to control the external characteristics of converters in DC microgrids to improve its inertia and damping feature. The small signal model of the proposed control strategy is built to identify the stability and dynamic characteristic. In order to eliminate the abrupt change in the beginning of the voltage dynamic characteristic, a feedforward control is implemented and the dynamic characteristic is revised. Then by analyzing system stability, the range of virtual inertia control coefficient and damping control coefficient are determined. Finally, hardware- in-the-loop (HIL) simulation based on RT-LAB is carried out to verify the validity of the above theoretical analysis and control strategy. In this simulation, the proposed control strategy is implemented in the energy storage system, which provides inertia support to smooth the DC voltage under power fluctuations.

An Inertia and Damping Control Method of DC–DC Converter in DC Microgrids

A novel droop control with coupling compensation and inertia is proposed for a microgrid to achieve high dynamic performance and stability of distributed generation units. The coupling compensation scheme consists of angular frequency deviation compensation and voltage deviation compensation. They can reduce the influence of uncontrolled power coupling. The inertia scheme consists of angular frequency inertia and voltage inertia. They can slow down the change rates of the angular frequency and voltage and reduce their fluctuation magnitudes. The combination of this novel droop control method and virtual impedance can help achieve accurate power sharing. An improved particle swarm optimization (PSO) algorithm with multiswarm and multivelocity (MMPSO) is also proposed to optimize the parameters of the coupling compensation and inertia with high precision and high reliability. A simulated model and experiment platform of a microgrid are set up for testing, and the simulation and experimental results validate the excellent performance of the MMPSO and the effectiveness of the novel droop control method.

The Application of Microgrids Based on Droop Control With Coupling Compensation and Inertia

This paper presents the integration of the battery and photovoltaic (PV) system and the adaptive control strategy for power balance and the intermittency mitigation in residential dc microgrid system. The excessive power leads to the overvoltage in the dc bus when available power from PV arrays is greater than the sum of the load power. While clouds pass over the panels, the dc bus becomes dynamically unstable. This paper is proposing the adaptive control strategy in residential dc microgrid to stabilize the dc bus and prevent over-voltage issues. The circuit topology has been selected as a suitable candidate for dc distribution system in residential applications. The implemented circuit topology provides two main dc bus voltage levels for residential applications, 48 V dc, and 400 V dc, and a 100 V dc intermediary bus for power transfer from one bus level to the other. The circuit topology consists of a boost converter for a PV power generation, a buck-boost converter for both discharging and charging the battery from 100 V dc bus, and a bidirectional half-bridge converter to regulate 400 V dc bus. The proposed adaptive control strategy monitors the PV power generation, dc load power demand and optimizes the state of charge (SOC) of the battery in order to constantly balance power generation and the load power demand accordingly. The simulation and experimental results reported in this paper verify the dynamics and performance of the proposed adaptive control strategy for PV-battery system in residential dc microgrid. This control strategy has been implemented and verified in A 2 kW prototype.

An adaptive control strategy for power balance and the intermittency mitigation in battery-PV energy system at residential DC microgrid level

A virtual synchronous generator (VSG) control for high power permanent magnetic synchronous generators (PMSG) in wind power generation is investigated in this paper A power factor correction (PFC) rectifier for each phase of the PMSG is designed to transform variable voltage and frequency of wind power into constant voltage DC power The PFC boost inductor is replaced by a PMSG armature inductance to reduce the size and cost of the overall system A three-phase inverter is used as a power interface to feed the generated wind power to the grid or load By designing an excitation controller and a prime motor controller, the PMSG-based wind power interface can mimic a self-stabilization characteristic of synchronous generator which has rotor inertia, thus helping to improve the stability of wind power generation Experimental results of the VSG inertia performance are illustrated, and the simulation results of traditional PQ and proposed VSG control are given and compared to validate the proposed converter topology and control algorithm

Control strategy of high power converters with synchronous generator characteristics for PMSG-based wind power application

In general, residential solar inverters can operate in either island or grid-tied mode. In grid-tied mode, the inverter can be operated based on either voltage control or current control. In this paper, a grid-connected current controlled inverter is presented. A stationary frame nonideal proportional resonant (PR) controller, in lieu of a conventional PI based controller, is applied to the outer current control loop to eliminate the steady-state error between the given reference and the inverter current output. The reference signal is directly given to satisfy the expected power output. The voltage source inverter (VSI) control system, reported in this paper, can estimate the instantaneous active and reactive power (PQ) based on a revised orthogonal signal generation (OSG) structure and control the power flow through a PQ controller in grid-connected mode. Thus, the solar inverter is able to work as a reactive power compensator, which helps lower transmission losses and improve grid power factor. Compared with traditional V/f based PQ controller and fuzzy-PQ controller, the proposed current based PQ controlled grid-tied inverter provides the system with faster reference tracking response and better power decoupling capability. Analysis and simulation results are presented in this paper to validate the proposed system.

Residential renewable energy distribution system with PQ control

An isolated photovoltaic converter for residential use and its control strategies are investigated in this paper. This technique provides galvanic isolation and simplified control while still meeting high conversion efficiencies and wide input voltage range requirements. Through designing the equivalent resonant capacitor and inductor, zero-voltage switching (ZVS) and zero-current switching (ZCS) are realized. Efficiency is dramatically increased by reducing the circulating energy during each switching cycle. In order to analyze the resonant converter and achieve better performance, an optimal state-trajectory control is investigated and implemented. To significantly reduce the voltage error and achieve a better transient response for the grid-tied mode operation, the proposed direct-quadrature (D-Q) frame control is used instead of a normal PID control for the inverter. Simulation and experimental results reported in this paper verify the functionality of the proposed topology and the respective controller for optimizing efficiency and performance.

Optimizing efficiency and performance for single-phase photovoltaic inverter with Dual-Half Bridge converter Yuzhi Zhang

A new power conversion architecture for a residential power router is reported In comparison to previously published architectures, this one offers higher efficiency and performance, and is more amenable to production for the emerging mass consumer market for systems to manage energy harvesting, storage, and consumption The integrated system includes the hardware for dc-to-ac power conversion and system level controls for power flow and load management For the hardware, the tracking resonant frequency (TRF) and direct-quadrature (D-Q) controls are respectively implemented in dual-half bridge (DHB) to increase the system efficiency, and in the inverter to reduce the voltage error For the system level controls, the power flow management is developed based on a rule-based algorithm using real-world time-of-use (TOU) electricity pricing data parsed from the Internet through the LabVIEW™-based communication interface The simulation and experimental results reported in this paper verify the efficient dc/ac power conversion and the optimized performance of the integrated residential energy harvesting and management system

Haoyan Liu

Papers

Control strategy of high power converters with synchronous generator characteristics for PMSG-based wind power application

Residential renewable energy distribution system with PQ control

Optimizing efficiency and performance for single-phase photovoltaic inverter with Dual-Half Bridge converter Yuzhi Zhang

Realizing an integrated system for residential energy harvesting and management