Jie Chen

Bio: Jie Chen is an academic researcher from Nanjing University of Aeronautics and Astronautics. The author has contributed to research in topics: Voltage droop & Power optimizer. The author has an hindex of 12, co-authored 43 publications receiving 750 citations. Previous affiliations of Jie Chen include Nanjing University.

Impedance-Phased Dynamic Control Method for Grid-Connected Inverters in a Weak Grid

Abstract: A power distribution grid exhibits the characteristics of a weak grid owing to the existence of scattered high-power distributed power-generation devices. The grid impedance affects the robust stability of grid-connected inverters, leading to harmonic resonance, or even instability in the system. Therefore, a study of the stability of grid-connected inverters with high grid impedance based on impedance analysis is presented in this paper. The output impedance modeling of an LCL -type single-phase grid-connected inverter is derived, where the effects of the PLL loop and the digital control delays on the output impedance characteristics have been taken into account. To enhance the stability of grid-connected inverters with different grid impedance, a novel impedance-phased compensation control strategy is proposed by increasing the phase margin of the grid-connected inverters. Specifically, a detailed implementation and parameter design of the impedance-phased compensation control method is depicted. Finally, an impedance-phased dynamic control scheme combined with online grid impedance measurement is introduced and also verified by the experiment results.

Investigation on the Selection of Electric Power System Architecture for Future More Electric Aircraft

Abstract: This paper identifies the most promising electric power system (EPS) architecture for a future more electric aircraft based on reviews and evaluations of both system weight and stability feature of the existing EPS architectures. When comparing the overall system weight of different architectures, various aspects, including voltage generation, wiring system, ground operation, power conversion, and complexity of integrating alternative energy sources, are considered. After choosing the possible candidates among all the possible architectures by using weight-saving criterion, stability features for the initially selected candidates are further evaluated. Necessary simulation studies are carried out in MATLAB/Simulink to prove the correctness of stability study. Finally, the one both good at weight saving and with the highest stability region is deemed as the most promising EPS architecture for future MEAs.

New Overall Power Control Strategy for Variable-Speed Fixed-Pitch Wind Turbines Within the Whole Wind Velocity Range

Abstract: Variable-speed fixed-pitch (VSFP) wind turbines have good prospects in small-to-medium-scale wind power markets due to their simple structure, low cost, and high reliability. One difficulty with VSFP concept wind turbines is to prevent overspeeding and overloading problems at excessive wind velocities, which has rarely been reported in literatures until now. This paper first proposes a sensorless overall power control strategy for a commonly used permanent-magnet-synchronous-generator-based VSFP concept wind power system, with which maximum power point tracking operation, constant speed stalling operation, and constant power soft-stalling operation are all realized. The proposed control scheme has a special advantage of simple structure, i.e., only two regulators are used to realize the three operational modes and also the natural transition between them. An aerodynamic power observer is adopted in the proposed scheme to fasten the MPPT speed. In addition, to enhance system robustness to parameter variations and optimize dynamic and static speed-control performance, an adaptive PI-like fuzzy logic controller is proposed and used as speed regulator in the overall power control scheme. The proposed strategy is verified by simulation and experimental results performed by a 1.2-kW VSFP concept wind turbine prototype.

Stability Analysis and Parameters Optimization of Islanded Microgrid With Both Ideal and Dynamic Constant Power Loads

Abstract: In this paper, a framework for stability analyses of a typical inverter-based islanded microgrid with two types of nonlinear loads is presented, namely ideal constant power loads (CPLs), which are the loads supplied by tightly regulated power electronics converters, and dynamic CPLs, which are used to represent motor-drive systems with large time constants. The comprehensive dynamic model of the considered microgrid is first developed, based on which a bunch of small-signal models are deduced using Taylor expansion made at different stable operating points. Afterward, eigenvalue-theorem-based stability analysis and parametric sensitivity analysis are successively performed on the obtained small-signal models to verify the stability of the system, predict the system's unstable regions, and identify the effects of parameters on the stability boundaries. In the meantime, the impacts of different kinds of nonlinear loads on the system stability are studied. Hardware-in-the-loop (HIL) real-time simulation platform of a 30-kVA microgrid, which is mainly formed by a 10-kVA photovoltaic (PV) system, a 10-kVA wind energy conversion system, a 10-kVA lithium-ion battery energy storage system, and two CPLs, is established in Typhoon HIL 602 device. The validity of the theoretical results is verified by real-time simulation results.

On Optimizing the Aerodynamic Load Acting on the Turbine Shaft of PMSG-Based Direct-Drive Wind Energy Conversion System

Abstract: The blade's rotational sampling to the spatial distributed wind velocities will induce 3P oscillating aerodynamic torque during the wind energy generation process. This causes the turbine drive train bare high aerodynamic load because the generator is driven by this aerodynamic torque through it. Moreover, the system's inherent resonant mode will be also induced by the aerodynamic load, causing fatal damage to the whole system. To damp the serious aerodynamic load of the permanent-magnet-synchronous-generator-based direct-drive wind energy conversion system (WECS), a new power control strategy with damping injection is proposed in this paper. The proposed method is realized by adding a compensation torque, which is proportional to the small-signal value of the generator speed, into the system torque control loop. Both the aerodynamic load and the system's inherent resonant mode could be well damped if the proposed method were adopted. Theoretic analysis is verified by experimental results performed by a 10-kW WECS established in the laboratory.

Distributed Economic Dispatch for Smart Grids With Random Wind Power

Abstract: 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.

Power Control in AC Isolated Microgrids With Renewable Energy Sources and Energy Storage Systems

Abstract: This paper presents a new strategy to control the generated power from energy sources existing in autonomous and isolated microgrids. In this particular study, the power system consists of a power electronic converter supplied by a battery bank, which is used to form the ac grid (grid former converter), an energy source based on a wind turbine with its respective power electronic converter (grid supplier converter), and the power consumers (loads). The main objective of this proposed strategy is to control the state of charge of the battery bank limiting the voltage on its terminals by controlling the power generated by the energy sources. This is done without using dump loads or any physical communication among the power electronic converters or the individual energy source controllers. The electrical frequency of the microgrid is used to inform the power sources and their respective converters about the amount of power that they need to generate in order to maintain the battery-bank charging voltage below or equal its maximum allowable limit. Experimental results are presented to show the feasibility of the proposed control strategy.

A Distributed Control Strategy for Coordination of an Autonomous LVDC Microgrid Based on Power-Line Signaling

Abstract: In a microgrid (MG), an energy management control is essential in order to handle the variety of prime movers, which may include different types of renewable energy sources (RESs) and energy storage systems (ESSs). Specifically, the recharging process of the secondary battery, i.e., the most prominent ESS, should be done in a specific manner to preserve its lifetime, the common MG bus voltage must be kept within the bounds, and the energy offered by RES should be utilized as efficiently as possible. This paper proposes a method for coordination of an autonomous low-voltage direct-current (LVDC) MG that consists of a number of sources using power-line signaling (PLS), which is a distributed control strategy in which the units inject sinusoidal signals of specific frequency into the common bus in order to communicate with each other. The control structure that allows the application of this method is revealed, and the optimal range of operating PLS frequencies is specified. In order to achieve a zero steady-state error of injected signals in the common bus, primary control of batteries has been extended with dedicated proportional-resonant controllers that are switched on only during injection period. Finally, a method for coordination among the units using the PLS concept was developed and experimentally tested, confirming its applicability for autonomous LVDC MGs.

An Improved Feedforward Control Method Considering PLL Dynamics to Improve Weak Grid Stability of Grid-Connected Inverters

Abstract: Phase-locked loop (PLL) is commonly used for three-phase grid-connected inverters to obtain the information of grid synchronization, and PLL dynamics are the key factors for stable operation of the inverters. Under weak grid conditions, the coupling between PLL and grid impedance can result in harmonic resonance, or even instability in the system. In this paper, the effect of PLL dynamics and grid impedance on the stability of three-phase grid-connected inverters is studied with the d – q impedance model. Besides, the variable transfer relationship is used to analyze the influence of PLL perturbations on output current under weak grid conditions. To suppress low-order harmonics of the network current caused by PLL perturbations under weak grid conditions, a novel feedforward control method is proposed to compensate PLL perturbations and revise the output impedance, where the operation of the inverter and PLL dynamics have been taken into account in the design process. By analyzing the impedance characteristic of the system, it can be demonstrated that the proposed method can enhance the stability of grid-connected inverters under weak grid conditions and reduce the impact of PLL perturbations on grid-connecting current. The experimental results indicate that the low-order harmonics of the network current can be suppressed effectively, which verifies the analysis.

On-Board Microgrids for the More Electric Aircraft—Technology Review

Abstract: This paper presents an overview of technology related to on-board microgrids for the more electric aircraft. All aircraft use an isolated system, where security of supply and power density represents the main requirements. Different distribution systems (ac and dc) and voltage levels coexist, and power converters have the central role in connecting them with high reliability and high power density. Ensuring the safety of supply with a limited redundancy is one of the targets of the system design since it allows increasing the power density. This main challenge is often tackled with proper load management and advanced control strategies, as highlighted in this paper.