Gallium nitride (GaN) devices have great potential in high-frequency and high power density converters. And GaN devices are more and more used into synchronous rectifier circuits. However, the high switching speed of GaN device makes it prone to have switching oscillation problems. Considering the low loop damping determined by the low on-resistance characteristic of the device and compact PCB design, the oscillations can even be sustained, affecting the circuit stability. In order to solve this problem, RC damper is paralleled to the drain-source of the synchronous rectifier device. The suppression mechanism is explained from the aspect of loop conductance matching based on oscillator theory. And a modified negative conductance model of the GaN-based synchronous rectifier circuit is established. Based on the established model, the optimized design method of the RC parameters is proposed. The method is verified to be effective by experiments. In addition, power loss analysis of the RC damper has also been analyzed.

With the engineering realization and further development of maglev trains, the lifetime prediction of its main power unit, i.e., insulated gate bipolar transistor (IGBT) module, attracts much popularity. However, the complex operating conditions of maglev trains cause the lifetime of IGBTs to be affected by a combination of factors. And the analysis of a single factor will lead to inaccurate lifetime prediction. To address this, for the IGBT of the maglev trains, this paper proposes a lifetime prediction model that considers the effect of changing practical conditions and device aging. In this method, the ambient temperature change of the maglev train in a year and the change of the on-resistance during the aging process is taken into account. Meanwhile, in the system perspective, the effects of changes in voltage levels and switching frequencies are included. And the coupling effects of multiple factors are thoughtfully analyzed and introduced into the lifetime prediction model, which improves the accuracy of the lifetime prediction. Finally, the results of the factor impact analysis and lifetime prediction are validated by power cycling experiments and real vehicle operation data.

Second-order harmonic current (SHC) inevitably presents in the two-stage AC/DC and DC/DC system, e.g., solid-state transformer (SST) cell. Unregulated harmonics routing leads to reliability defects, which may appear in DC-link and DC/DC stage. This manuscript presents a reliability-oriented design method via routing the SHC. Firstly, the SHC distribution in the two-stage SST cell is modeled, and their effects on the reliability of DC-link capacitor and DC/DC stage are revealed. Interactions are highlighted between the reliability of DC-link and DC/DC stage. It illustrates that a small capacitance may favor the DC-link reliability, yet jeopardizing the overall system. A tradeoff analysis is performed to achieve longer mean time to failure (MTTF) on an SST cell level. The harmonic distribution unravels a new mechanism that governs the reliability balance between critical components. It also provides an alternative perspective to the reliability-oriented design. The distribution model and design framework are performed in a 15 kW SST cell.

Among various speed-sensorless control methods for induction motors (IMs), phase-locked loop (PLL)-based speed estimation schemes (SESs) have become attractive due to the advantages of easy implementation and good flexibility. However, most of the PLL-based schemes with the proportional-integral (PI)-based loop filter may lead to obvious performance degradation under acceleration and deceleration operation modes. To address this, in this paper, a four-consecutive-samples (FCS)-based SES is developed for IMs to achieve accurate estimation. The proposed SES uses the rotor flux and its delay signals, instead of solely increasing the system order. Additionally, considering the adverse effects of disturbances on the estimation performance of the proposed SES, a closed-loop flux observer (CLFO) that is able to provide high robustness against disturbances, is introduced to the proposed SES. The performance of the proposed SES is experimentally investigated on a case study system.

To improve pure integral calculations with integral drift and dc bias, and poor dynamic response under conventional direct power control, a grid-voltage sensorless predictive current control strategy of three-phase PWM rectifier is proposed. In the voltage sensorless control algorithm, an improved virtual flux observer is constructed by introducing bandstop filter feedback to solve the dc bias. Moreover, to address the inaccurate voltage-vector selection algorithm in the two-step prediction, Lagrange interpolation is introduced to make the predictive current more accurate. Experimental results verify that the three-phase PWM rectifier with the proposed strategy can achieve high power factor, high prediction accuracy and improve dynamic performance of the system.

Due to manufacturing process immaturity, the parameter dispersion of Silicon Carbide (SiC) MOSFET is severe, which has risks of current imbalances and oscillation in parallel applications. In addition, as the bipolar degradation is gradually solved, SiC MOSFET body diodes are used to replace anti-parallel diodes to conduct at dead time. Therefore, the screening method needs to consider the current sharing capability in dynamic, static, and reverse processes at the same time. This article analyzes the body effect of SiC MOSFET and the feasibility of taking output curves at multiple gate voltages as screening objects. Then, the concept of multivariate statistical analysis is introduced to quantify the similarity of output curves into distance parameters, and an automatic screening method based on hierarchical clustering is proposed. The validity that the distance parameters at room temperature can be used in a wide temperature range (25–150 °C) is evaluated. Finally, a double pulse test platform with a highly symmetrical circuit is built to test the performance between the proposed method and traditional screening methods. As a result, the error between paralleled devices selected by the proposed method is less than 5% in dynamic and reverse processes and 2% in static processes simultaneously.

The estimation of insulated gate bipolar transistor (IGBT) module lifetimes in electric vehicle (EV) converters is heavily influenced by long-term mission profiles (MPs), as their reliability is significantly affected by power fluctuations. This paper presents a lifetime estimation method for IGBT modules based on MPs, using a 115 kW electric drive system as a case study. First, considering the standard road spectrum for EVs, the mathematical model of an automotive motor, and its control strategy, the load conditions for the converters are calculated. Next, employing an electro-thermal coupling model of the power device, the power loss and junction temperature characteristics of the IGBT modules for EV converters under specific load conditions are analyzed. Subsequently, the consumed lifetime is determined using a physics-of-failure-based lifetime model and cumulative damage theory. Finally, the paper delves into the reliability-oriented control strategies of EV converters, which fully utilize the transmission ratio of the EV to enhance the IGBT module's lifetime. Test results demonstrate that, by employing the optimal transmission ratio, the lifetime can be extended by more than two times compared to the initial estimation value.

Single phase inverters/rectifiers have double-frequency voltage ripple on the DC-link due to the unbalanced instantaneous power between the input and output. In extremely low frequency detection and communication systems, the output frequency of the power amplifier is low and variable. The low output frequency limits the cutoff frequency of the filter and thus causes a delay. Meanwhile, variable output frequency limits the application of ripple frequency sensitive methods such as proportional-resonant control. This paper proposes a general power decoupling control method independent of the ripple frequency and supporting plug-in operation. Firstly, this paper analyzes the characteristics of DC-link voltage ripple and the power decoupling control method based on the DC-link capacitor current is proposed. Then, the effects of capacitor equivalent series resistor and DC source output capacitor on the control method are analyzed in detail and corrected. In addition, the stability of control system and parameters designed are described. Finally, a 3 kW experimental prototype is designed to verify the validity and correctness of the analytical control method.

To solve the problem that the switching frequency is not fixed for five-level nested neutral point piloted (NNPP-5L) converter with classical model predictive control (MPC), an optimized MPC using a multi-vector (MV)-MPC for an NNPP converter with constant switching frequency (CSF) is proposed. First, the mathematical model of NNPP-5L is established, and then a cost function without weighting factors is designed based on the optimized MPC to select the four optimal voltage vectors. Next, the duty time of the four optimal voltage vectors is calculated from the cost function, and the optimal switching sequence with a symmetric seven-segment pulse pattern is generated using a modulator to balance the voltage of capacitors. This strategy offers the advantage of a CSF and computation burden reduced while maintaining the dynamic response of the MPC for NNPP-5L converter. Finally, the effectiveness and feasibility of the proposed MV-MPC for NNPP-5L converter have been validated by simulation analysis and experiment results.

With the growing maturity of new energy power generation technology, the requirements of boost link in the system are also getting higher and higher. In this study, a new coupling inductor voltage multiplier is proposed, series it with several boost converters, which can get a family of coupled inductor voltage-multiplying boost converters. The voltage gain is significantly improved, the voltage stress of the device is also significantly reduced, and the leakage inductance generated by the coupling inductor can be absorbed, which can restrain the voltage spike of power switch, reduce electromagnetic interference (EMI). This paper analyzes the working principle, steady-state characteristics, parasitic resistance, system stability and other aspects of the converter in detail. Finally, taking one of the converter topologies as an example, its good performance is verified by the experimental results based on a 200 W experiment prototype.