Xuefang Lin-Shi

The modular multilevel converter (MMC) is a critical component in modern medium- and high-voltage systems, whose reliability is severely compromised by open-circuit faults (OCFs) in insulated gate bipolar transistors (IGBTs). Consequently, accurate real-time fault diagnosis is essential to ensure safe and reliable operation. However, diagnostic accuracy is often compromised by the variability of fault characteristics under different operating conditions. Therefore, a hierarchical diagnosis method based on the arm capacitor voltage span (ACVS) is proposed. First, the adjacent-cycle ACVS values are analyzed to construct an adaptive threshold. A three-level localization scheme is then implemented: the faulty arm is detected via abnormal ACVS deviation; the faulty submodule (SM) is located by analyzing the voltage differences between adjacent SMs after sorting; and the faulty IGBT is identified based on the switching state of the faulty SM. As only a small number of voltage data are processed, the online computational burden is reduced. The proposed method is validated through both simulation and experiment under different operating conditions. The faults are located in less than 20 ms, and an overall accuracy of 0.99 is achieved in the tested scenarios. The results show that fault diagnosis can still be achieved under arm inductance mismatch and load transients.

Tidal energy is increasingly harnessed due to its high energy density, substantial reserves, and reliable predictability. However, marine fouling on turbine blades adds weight and induces asymmetric system loads; prolonged operation exacerbates generator magnetic saturation, causing inductance parameter deviations from controller presets, which further leads to current loop delays, amplified tracking errors and unstable power output. To mitigate these issues, a self-tuning inductance-oriented model-free predictive current control method is proposed. The proposed method utilizes a simplified hyperlocal model alongside an extended state observer to effectively counteract the effects of non-inductive parameters. Simultaneously, the incremental model coupled with a dynamic adjustment method is proposed for real-time adaptive inductance tuning. Simulation results demonstrate that the proposed method significantly enhances system robustness against inductance mismatches and reduces parameter sensitivity, thereby ensuring stable operation. Compared with traditional PI control and model predictive control strategies, the proposed approach exhibits superior performance in disturbance rejection, parameter adaptability, and operational stability.

Single-Input, Multi-Output (SIMO) converters present significant challenges when operated under current-mode control, due to their strongly non-linear dynamics and susceptibility to bifurcation phenomena. To mitigate the effects on the converter’s steady-state, a double slope compensation solution is proposed. The compensation parameters play a critical role in shaping the system dynamics and rejecting the susceptibility to bifurcation. This paper proposes a detailed analysis methodology to investigate the design parameter space regarding the slope compensations with respect to bifurcation phenomena. The approach is validated on a CMOS integrated converter, where theoretical predictions are compared to the simulation results of a full transistor-level model of the circuit.

In automotive applications, industrials use DC-DC boosting stages interfaced upstream of the Voltage Source Inverter (VSI) to increase the DC bus voltage. These topologies enable the motors to be driven with higher DC bus voltage than that delivered by the battery. Apparently, the use of extra DC-DC converter decreases the efficiency of the whole system. Recently a single-stage topology called the Split Source Inverter (SSI) was derived. This topology enables the boosting function. Unfortunatly, it exhibits very poor utilization of the DC bus voltage, thus preventing its use for traction applications. In previous work, the authors introduced a new single-stage topology called the Bidirectional Active Split Source Inverter (B-ASSI). It enables the boosting function with bidirectional power flow capability and a large utilization of the DC bus voltage. However, its efficiency was not thoroughly studied and comparison with conventionnal two-stage solution not conducted. This paper proposes an in-depth losses analysis of the B-ASSI. Analytical expression of the currents are proposed and validated by simulation. An extensive experimental validations are carry out on a permanent magnet synchronous machine (PMSM) test-bench. The derived expressions and proposed approadh enables a theoretical comparison of the B-ASSI to two-stage solutions and to the SSI but also giving insights about the design of the converter. This theoretical comparison is performed on a normalized driving cycle. It demonstrates that for the given design constraints the B-ASSI exhibits lower losses than the classical two-stage solution and the SSI for low-speed operating conditions corresponding to urban drive profiles.

In the sliding-mode control of switched systems, the mode-dependent sliding surface is generally considered to fulfill performance requirements of different subsystems. However, in the mode-dependent sliding surface design, the system state may oscillate among subsliding surfaces, which affects both stability and robustness. To solve this issue, this article starts from ensuring the reachability of each subsliding surface and proposes the reachability-guaranteed sliding-mode control for asynchronously switched uncertain systems. First, a type of asynchronous mode-dependent sliding surface is designed. Then, the control law is novelly proposed upon the allowable maximum settling time based on the fixed-time theory, and a new criterion is given to address the reachability of each subsliding surface within the mode-running interval. Stability is analyzed for the closed-loop system under restricted switchings, and solvable inequalities are presented for the optimization of the controller gain. Finally, implementation to the Chua's circuit validates superiorities of the proposed method.

In the aero-engine control, fast response capability is significant in transient performance, especially when aircraft work in emergency scenarios. To improve the response speed of aero-engines, this brief proposes a type of fixed-time control using the switched system approach. First, aero-engines are modeled as switched systems to better reflect the multimode characteristics under various operating tasks. Then, the fixed-time controller is proposed, which has advantages of small computation and easy implementation. Novel criteria are proposed for fixed-time stability analysis of the closed-loop system under restricted switchings. Furthermore, specific calculations are provided to derive the upper bound for the convergence time. Finally, superiorities of the proposed method are validated through experimental results.

This paper proposes a boost-type four-leg inverter for three-phase permanent magnet synchronous machine (PMSM) drives where the power supply is innovatively connected between the neutral point of the motor and the fourth leg. Due to the special connection, the zero-sequence circuit of a PMSM drive fed by the proposed four-leg inverter can not only be used to tolerate an open-phase fault (OPF) but also to boost the dc-bus voltage. According to the analytical modelling and equivalent circuit, it is revealed that the four-leg inverter based PMSM drive is similar to a two-stage drive under healthy operating conditions. When an OPF occurs, the motor can be normally operated with only two active phases. In post-fault conditions, the remaining phase-currents are not sinusoidal any more. Besides, the trajectory of the post-fault current vector is not a standard circle. The traditional field-oriented control strategy can still be adopted in the drive. However, the references of the $d$ -axis current and neutral current have to be modified by injecting specific components. A differential flatness-based controller is proposed to track the time-varying current references. Experiments are carried out on a 1.2 kW PMSM test-bench to verify the effectiveness of the proposed scheme.

This article considers a robust output set-point tracking problem for an $m$ -terminal power flow controller (PFC) for meshed dc micro-grids. The PFC is a power electronics device used to control the power flow at a node in the meshed grid and may act as a dc circuit breaker. The system is modeled by state-space bilinear dynamics coupled with a polynomial output. In the proposed design, the plant is first extended with an integral action processing the regulation error. The cascaded model composed of the plant and the integrator is then stabilized using a saturated state-feedback law, designed with a forwarding approach. An anti-windup function is added to cope with transient saturations. A tuning method is proposed to set the controller gains along the available degrees of freedom with respect to a cost function. The stability of the closed loop is guaranteed for any compact set of initial conditions and for small parametric variations around the nominal set point. Experiments have been carried out and these properties are successfully assessed on a tenth-scale experimental setup.