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This article presents two power converters with controllers attached to the Free‐Piston Stirling Linear Generator (FPSLG) and energy storage system (ESS). The rectifier uses hysteresis‐SVPWM current regulation and CB‐SPWM, while the buck‐boost converter utilizes the dual‐loop PI control method. The storage battery receives energy from a linear‐generator with a rectifier and converter. The FPSE and linear motors in the FPSLG convert thermal to electrical energy. A two‐level electrical energy conversion technique using a three‐phase AC signal to DC and DC‐DC converter has been devised to reduce output electrical energy oscillation as well as stabilize the generating system's DC power. Initially, the FPSE's nonlinear model and the three‐phase permanent magnet linear‐motor's linear mathematical model were created and followed by the ESS and control mechanism simulation. The simulation shows that the ESS system and control approach can give stable power to the storage battery using linear‐generator power. The PR controller replaces the PI controller in the position loop to improve frequency and displacement tracing. The control system design was simulated in MATLAB and the topology's feasibility and correctness were confirmed. Comparative analysis shows that, rectifier uses the H‐SVPWM's unity power factor of AC and stability controllability of the DC‐side voltage is better than the CB‐SPWM approach. [ABSTRACT FROM AUTHOR]

In recent years, the wind energy conversion system faces significant challenges for stable and secure operations, especially in the weak grid due to high penetration of wind energy into the grid. Doubly fed induction generator (DFIG) is one of the most popular wind turbine generators due to its cost‐effective variable speed and low‐cost partial size power converter. Impedance interaction between series or parallel compensated weak grid and the DFIG system causes sub‐synchronous resonance (SSR) and high‐frequency resonance (HFR). A comprehensive review of the state‐of‐the‐art SSR and HFR in the DFIG system under a weak grid is presented. First, based on features, such as supplementary hardware, linear and non‐linear control strategies, the resonance damping techniques are classified into different types. Then, the advantages and disadvantages of SSR analysis and damping techniques techniques are put forward. Moreover, the latest development of state‐of‐the‐art SSR and HFR analysis and damping techniques are supplemented. Finally, the contemporary and future trends of the SSR and HFR techniques are discussed. [ABSTRACT FROM AUTHOR]

The online detection of incipient faults for permanent magnet synchronous machine (PMSM) has been a great challenge in recent decades, where the fault features are extremely trivial and the machine fault type is normally unknown in advance. An online fault detection and discrimination of incipient faults for PMSM, including stator interturn short-circuit and resistive unbalance fault, is proposed in this article. First, zero-sequence voltage signal is collected and the zero-sequence voltage component (ZSVC) is used to detect the abnormal status of the PMSM. Then, high frequency (HF) signals are injected to the PMSM to discriminate the fault type. It shows that the amplitude of the HF component in ZSVC is proportional to the frequency of the injected signal under interturn short-circuit while it is constant under the resistive unbalance fault, and due to this difference, the fault type may be discriminated. Finally, the effectiveness of the theoretical analysis is validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Summary: The doubly fed induction generator (DFIG) system is prevalent in the wind power industry due to cost‐effective variable speed operation and part size power converter. The DFIG system dynamic performance might be degraded by oscillations of the electromagnetic torque and instantaneous stator power under grid faults. This paper proposes an improved method to augment the dynamic performance of the DFIG system under the aforesaid scenarios, where an additional cascade converter (CC) is serially connected at Y‐point of DFIG stator windings. The DFIG performance under low‐voltage ride through (LVRT) and high‐voltage ride through (HVRT) is improved with the proposed control topology. Additionally, with auxiliary control provision, the proposed method can improve the stability of the DFIG system. The theoretical analysis and Matlab/Simulink simulations validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The advantages, such as the mature control method, less volume of the converter and generator, make the doubly fed induction generator system prevalent in the wind power industry. Nevertheless, the doubly fed induction generator is more susceptible to grid faults and disturbances. The instantaneous high voltage fault may occur due to the excessive local reactive power after the doubly fed induction generator system achieving low voltage ride through, and then the wind turbine might be disconnected again. Hence, not only the low voltage ride through but also high voltage ride through capability should be required for the doubly fed induction generator system to meet the grid code requirements. A comprehensive review of the state of the art low voltage ride through and high voltage ride through technologies for the doubly fed induction generator system is presented. Firstly, different types of common low voltage ride through and high voltage ride through techniques are classified according to their features, i.e. auxiliary hardware, linear or nonlinear control strategies etc. The pros and cons of different low voltage ride through and high voltage ride through techniques are given. Furthermore, the latest developments of low voltage ride through and high voltage ride through technologies are introduced. Finally, the future trends of both the low voltage ride through and high voltage ride through technologies are discussed. [ABSTRACT FROM AUTHOR]

A new Single-sided Variable Flux Permanent Magnet Linear Machine with flux bridge in mover core is proposed in this paper. The flux bridge prevents the leakage flux from the mover and converts it into flux linkage, which greatly influences the performance of the machine. First, a lumped parameter model is used to find the suitable coil combination and no-load flux linkage of the proposed machine, which greatly reduces the computational time and drive storage. Secondly, the proposed machine replaces the expensive rare earth permanent magnets with ferrite magnets and provides improved flux controlling capability under variable excitation currents. Multivariable geometric optimization is utilized to optimize the leading design parameters like split ratio, stator pole width, width and height of permanent magnet, flux bridge width, the width of mover's tooth, and stator slot depth at constant electric and magnetic loading. The optimized design increases the flux linkage by 44.11%, average thrust force by 35%, thrust force density by 35.02%, minimizes ripples in thrust force by 23%, and detent force by 87.5%. Furthermore, the results obtained by 2D analysis are verified by 3D analysis. Thermal analysis is done to set the operating limit of the proposed machine. [ABSTRACT FROM AUTHOR]

In recent years, the doubly fed induction generator (DFIG) operates in a weak grid, rather than a strong grid due to the high proportion of wind energy into the power grid. The impedance interaction between the DFIG system and series and parallel compensated weak grid might cause the subsynchronous resonance (SSR) and high frequency resonance (HFR) in the DFIG system, respectively. Phase locked loop (PLL) is a popular grid synchronization technique, and the high bandwidth PLL can cause resonance at middle frequencies in the DFIG system. However, the impact of PLL types and their controller dynamics on the resonance in the DFIG system are not adequately researched. The impact of the PLL controller with different types, such as synchronous reference frame (SRF) and Lead/Lag PLL, is studied in this paper to fill this gap. Additionally, an improved PLL is proposed, which can guarantee the high phase margin and decrease the likelihood of the resonance at middle frequencies in the DFIG system under a weak grid. Moreover, the phase margin of the DFIG system impedance with an improved PLL is less sensitive to its controller parameters. Simulation and experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Summary: The interaction of impedance between the doubly fed induction generator (DFIG) system and series‐compensated weak grid gives rise to an issue of subsynchronous resonance (SSR). Likewise, the high‐frequency resonance (HFR) occurs when a DFIG system is connected to parallel‐compensated weak grid. This paper proposes an improved method to mitigate the caused resonance. The improved method, based on impedance modeling, utilizes an additional cascaded converter (CC) at Y‐point of DFIG stator winding with virtual impedance implemented at the CC control unit, which reshapes the DFIG impedance for effective mitigation of both SSR and HFR. The virtual impedance is disabled when DFIG operated in series‐compensated weak grid, while enabled when working in parallel‐compensated weak grid, which effectively damps the HFR. A detailed theoretical explanation and impedance modeling of the CC has been given. The effectiveness of the proposed method has been validated through MATLAB simulations based on a 2‐MW DFIG system. [ABSTRACT FROM AUTHOR]

Multilevel converters have good potential in high power and high voltage applications due to their advantages of reduced voltage or current stress on power devices. In recent years, hybrid multilevel converter (HMC) have attracted increasing attention since less equipment is required. In this paper, the topologies and evolutions of HMCs are presented, where five topology derivation ways are given by using basic cells in series-parallel/parallel-series. Some general topologies or structures that are used to generate higher levels are also deducted. Then many existing HMCs can be derived, and new topologies of the HMC might be inspired. The capabilities of neutral point and FC voltage balancing control are investigated. The performance of the selected FC-based HMCs is analyzed. Finally, the verifications of operation principle and control strategies for the derived HMCs are carried out. [ABSTRACT FROM AUTHOR]