Journal of Power Electronics最新文献

The low power density and high frequency loss of the core limits the miniaturization of high-frequency transformers (HFT) with an increase of the switching frequency. In this paper, a composite core with laminated nanocrystalline films and ferrite sheets is proposed based on the high saturation magnetic flux density of nanocrystalline and the low loss of ferrite. The two materials are laminated at a certain thickness ratio to form a composite unit. Then multiple layers of units are stacked to form the composite core. A homogenization model is established to calculate the equivalent permeability. Then the magnetic field strength of the composite core can be obtained, which can be used to calculate the magnetic flux density in different materials. An optimization model is built with the objective of optimizing the core loss and power density by adjusting the thickness ratio. Based on the non-dominated sorting genetic algorithm II (NSGA-II), it obtains the optimal thickness ratio. Simulation results show that the composite core increases the magnetic flux density from 0.3 T to 0.55 T over a ferrite core. A 100 V/200 V, 1 kW, 20 kHz composite core HFT prototype is developed. The power density is increased by 23.5% when compared to a ferrite HFT. The core loss is reduced by 37% when compared to nanocrystalline HFT, and the efficiency is increased from 94% to 96.5%.

This paper proposes a novel power-factor-correction system for the harmonic suppression of high-power equipment. It connects a PWM (pulse width modulation) rectifier and several uncontrolled diode rectifier units in parallel. The PWM rectifier is not connected to the load, and the power of the IGBT device is lower than that of the traditional PWM rectifier. The diode rectifier unit is connected in parallel without the loop current, which is convenient for expansion. The diode rectifier unit can still work when the IGBT fails, which enables high reliability. When compared to conventional APFs (active power filters), the proposed system only controls the grid current as a sinusoidal wave at the power frequency, without tracking harmonics, which makes the control simpler and the current THD (total harmonic distortion) lower. In this paper, the operating modes of the proposed parallel system are analyzed and the mathematical model of the circuit is derived. In addition, the corresponding control strategy is proposed and the parameters of the LCL are designed. Finally, simulations were carried out to demonstrate the superiority of the proposed parallel system when compared with the traditional APF, and a 60 kW experimental platform was built to demonstrate the feasibility of the proposed scheme.

Recently, the permanent magnet synchronous motors (PMSMs) are considered to be one of the best options for electrical motor due to their high power density and efficiency for various applications including industrial robot and smart mobility. However, the safety and reliability of the PMSM have not been verified sufficiently when compared to the conventional induction motor. The failure of electric motor can lead to catastrophic failure of entire system, so it is important to detect potential failure modes or signs in advance. In this paper, an accelerated life test was carried out to induce and investigate the failure modes of PMSM and various signals were monitored to detect the types of failure modes during the test. The shaft of the motor was radially loaded to accelerate the failure of PMSM. The phase current, temperature, displacement of the shaft, and vibration were monitored to estimate the health state of the motor. As a result, the bearing and the shaft were the most vulnerable components under radially loaded condition. Also, it is proved that the different failure modes can be successfully detected and classified by monitoring the phase current and vibration signal.

The low-harmonic (LOH) voltage of the DC link of three-phase voltage source converter (VSC) requires a large aluminum electrolytic capacitor for suppression under nonlinear AC current. Consequently, this work proposes an active decoupling control method combining DC-link LOH voltage closed loop and LOH current feedforward based on a DC–DC converter. This methodology effectively transfers the DC-link LOH voltage to the smaller-sized decoupling capacitor in the DC–DC converter, thereby reducing the number of capacitors required to stabilize of the VSC DC-link voltage. This work first investigates the relationship between the DC-link LOH voltage and the VSC nonlinear current. Second, a mathematical model for the decoupling capacitor voltage is derived, indicating that its voltage form is complex under nonlinear AC current, making direct voltage control arduous. Subsequently, the principle and design process of the proposed active decoupling control strategy are analyzed in detail. A dedicated fast-response filter structure is also utilized to extract the feedback LOH voltage and feedforward LOH current in the DC link. Meanwhile, a simple control strategy for the DC component of the decoupling capacitor voltage is proposed to improve the utilization of the decoupling capacitor. Finally, the effectiveness and correctness of the method are experimentally verified.

DC fault current limiters (FCLs) are of great significance to the safe and stable operation of DC distribution systems. Among the various FCLs, inductor-based FCLs play an important role. However, the issue of inductor saturation generally exists, which causes limitations in practical engineering applications. A novel LC-resonance-based FCL is proposed in this paper, which can suppress the inductor-saturation effect and create a natural zero-cross current for enhancing performance. In addition, it can cooperate with the AC circuit breaker (ACCB) to quickly cut off faults. A theoretical analysis and the parameter design of the proposed FCL are presented. Finally, a scaled-down experiment test platform is built, and experiment tests and simulation case studies are carried out to verify the working principle and superiorities of the proposed FCL.

This paper presents development of a hardware simulator for the DC–AC inverters of electric compressors (e-compressors). In general, early-release EVs often feature a nominal battery voltage of around 400 V. However, EVs with a 400 V battery have drawbacks such as slow battery charging speeds and limited driving distances. To overcome these drawbacks, the nominal battery voltage has recently been increased from 400 V to around 800 V. Accordingly, research on electrical components applicable to EVs with an 800 V battery has been conducted. However, research on the DC–AC inverter used in the e-compressor, as a core component of an electric air conditioning system for EVs with 800 V battery, is insufficient. Therefore, the development of a hardware simulator of DC–AC inverters for the e-compressors used in EVs with an 800 V battery is proposed in this paper. The validity of the proposed hardware simulator is verified by experimental results.

In view of the disadvantages of negative torque and low operation efficiency in the traditional direct torque control (DTC) for the switched reluctance motor drive (SRD), a novel DTC strategy based on optimal turn-on angle is proposed in this paper. First, the flux hysteresis controller of the traditional DTC is cancelled and the SRM is only controlled by the torque hysteresis controller. The actual rotor position angle is used to divide the sectors instead of the angle calculated by the stator flux, which does not need to select the optimal given flux value, and makes the division of sectors more in line with the inductance characteristics of the SRM. Second, the function for calculating the optimal turn-on angle is designed and the sectors are reallocated. The optimal voltage vector is selected according to the output signal of the torque hysteresis controller and sector position. Finally, the 12-sector DTC method is selected as comparison algorithm and the correctness of the proposed method is confirmed by simulation and experimental results. It is demonstrated that the proposed strategy retains the advantages of the simple structure of the traditional DTC. In addition, it eliminates negative torque, improves the DC bus voltage utilization and torque ampere ratio, and reduces the torque ripple, switching frequency and copper losses.

In the railway industry, there is ongoing research on incorporating large-capacity energy storage system (ESS) into railway vehicles to reduce carbon emissions and enhance energy efficiency. Lithium-ion batteries are widely used in ESSs due to their high energy density. However, their high chemical reactivity can lead to a higher risk of malfunction. This compromises the reliability of railway vehicles using a high-capacity ESS as a propulsion power source. This study aims to improve the reliability of the battery packs used in railway vehicles by introducing a novel circuit configuration that integrates a bypass circuit into the traditional redundant circuit configuration used in lithium batteries. In conventional ESS systems, an additional battery pack needs to be equipped to sustain normal operation in the case of a battery malfunction event. However, this leads to a substantial increase in the volume and weight of the ESS. The circuit configuration proposed in this paper guarantees the normal operation of the ESS in the case of a battery failure using a few additional circuit components. The feasibility of the proposed circuit configuration and its operation are examined using railway vehicle battery pack specifications.

This study proposes an on-line minimum loss (ML) control strategy that considers the iron and copper losses of an interior permanent magnet synchronous motor in torque-controlled applications. The proposed ML control strategy utilizes a constrained optimization problem to satisfy torque reference tracking and loss minimization. An equivalent iron loss resistance circuit is adopted for the loss minimization. To solve the optimization problem, the Lagrange multiplier method is applied through a numerical analysis algorithm. The resulting solution provides the optimal current reference for every sampling instant. The Lagrange multiplier method needs parameters such as magnetic flux linkages, dynamic inductances, and iron loss resistance. Fundamental magnetic flux linkages are estimated using a flux observer, and the dynamic inductances are estimated with high-frequency voltage signal injection. The proposed iron loss resistance estimator estimates the equivalent iron resistance without any preliminary experiments. DC input power is measured using a current sensor for the accurate on-line estimation of iron loss resistance. To analyze the effectiveness of ML control compared with conventional maximum torque per ampere control, finite element analysis is used. The feasibility of the proposed ML control strategy is verified through simulation and experiments.

Abstract

Model predictive control (MPC) is recognized as an efficient control method for the modular multilevel converter (MMC), owing to its advantages, such as good robustness, rapid dynamic response, and multi-objective control. However, due to the coupling relationship between the ac-side current and the circulating current, the existing MPC has an impact on the ac-side current while suppressing the circulating current. In this paper, the relationship between the ac-side current performance and circulating current suppression is discussed in detail, and a three-stage MPC (TS-MPC) strategy is proposed to optimize the comprehensive performance. With the ac-side current control, circulating current control, and comprehensive optimization control, the optimum performance of both the ac-side current and circulating current suppression is realized while maintaining a low computational burden. Moreover, a grouping sorting algorithm is designed to reduce the calculation burden and to balance the capacitor voltages. The steady-state and transient performances of the proposed TS-MPC strategy have been verified by experimental results, which validates its correctness and effectiveness.