Qiao Zhang

The rapid electrification of transportation has accelerated the demand for high-power electric vehicle (EV)-charging systems with high efficiency, compact size, galvanic isolation, and flexible scalability. Conventional isolated EV chargers typically adopt cascaded AC–DC and DC–DC conversion stages, which require additional semiconductor devices, passive components, and bulky dc-link capacitors, thereby increasing system complexity and limiting power density. This paper proposes a scalable three-phase modular parallel quasi-single-stage isolated single-ended primary-inductor converter (SEPIC) for high-power EV fast-charging applications. The proposed converter integrates power factor correction, voltage regulation, and high-frequency isolation within a unified SEPIC-based conversion cell, eliminating the intermediate dc-link capacitor while reducing the number of magnetic components and power conversion stages. By employing a Δ-connected three-phase input and input/output-parallel modular configuration, the proposed architecture provides a flexible power expansion approach based on a 9 kW basic module, with the potential to extend to higher power levels, such as 54 kW, through paralleling multiple identical modules. The operating principle, steady-state characteristics, continuous conduction mode (CCM)/discontinuous conduction mode (DCM) transition mechanism, current-sharing behavior, and control strategy are systematically investigated. An 18 kW prototype consisting of two parallel modules is experimentally validated under 380 V three-phase AC input and 400 V DC output conditions. The experimental results demonstrate a peak efficiency of 97.5%, a rated efficiency of 97.3%, a power factor (PF) of 0.999, and an input current total harmonic distortion (THD) of 2.55%, confirming the effectiveness and scalability of the proposed converter for high-power EV fast-charging applications.

Gallium Nitride High Electron Mobility Transistors (GaN HEMT) are widely used in high-frequency applications owing to their fast-switching speed and low switching loss. However, the large dV_DS/dt transients can cause severe crosstalk, current overshoot, and EMI issues. While conventional gate drivers can mitigate these issues by slowing down the switching process, the switching loss is significantly increased. To reduce the switching loss under dV_DS/dt limitation, this paper proposes a gate-side feedback active gate driver (AGD) to adaptively regulate the switching transient by providing three-stage driving currents. Switching points of the three-stage driving currents are determined by detecting the start of the Miller plateau through gate voltage slope and identifying its termination when the gate voltage exceeds the Miller plateau voltage. With the detected signal, the gate driving current during the Miller plateau is reduced to suppress dV_DS/dt and mitigate current overshoot. Under 400 V/20 A conditions, experimental results show that the proposed driver can effectively control dV_DS/dt and suppress current overshoot, while reducing the dV_DS/dt-related switching interval by 68.13% and switching loss by 51.8%, thereby confirming its effectiveness.

This paper proposes a digital predictive peak current control (PPCC) strategy for superbuck converters. The proposed strategy incorporates a current predictor to calculate the output current and a peak current controller to calculate the required duty ratio for the next switching cycle. The duty ratio is precalculated ahead of a switching cycle, which creates a switching cycle for signal samplings and digital calculations. At the end of the next switching cycle, the output current peak value is regulated to match the reference value. The proposed strategy regulates the output current peak value to the reference value within two switching cycles. This increases the current loop bandwidth to π/T rad/s, which optimizes the transient performance. Moreover, a new damping parameter design method based on the damping ratio is given. Furthermore, a simplified version is proposed to facilitate digital realization. This version directly calculates the required duty ratio, which significantly reduces digital calculations. Finally, the experimental results demonstrate the effectiveness of the proposed control strategy in improving the transient performance of the superbuck converter.

This paper proposes a gallium nitride (GaN)-based very-high-frequency (VHF) resonant flyback converter with integrated magnetics, which utilizes the parasitic inductance and capacitance to reduce the passive components count and volume of the converter. Both the primary leakage inductance and the secondary leakage inductance of the transformer are utilized as the resonance inductor, while the parasitic capacitance of the power devices is utilized as the resonance capacitor. An analytical circuit model is proposed to determine the electrical parameters of the transformer so as to achieve zero voltage switching (ZVS) and zero current switching (ZCS). Furthermore, an air-core transformer was designed using the improved Wheeler’s formula, and finite element analyses were carried out to fine-tune the structure to achieve the accurate design of the electrical parameters. Finally, a 30 MHz, 15 W VHF resonant flyback converter prototype is built with an efficiency of 83.1% for the rated power.

In this paper, a sample voltage dead-beat control based on differentiative voltage prediction (DVP) and switching-cycle extension (SCE) is presented to achieve optimal transient response for DC-DC converters under discontinuous conduction mode (DCM) operation. Firstly, to improve load transient response, a DVP method is proposed to estimate the load. With the estimated load, the controller realizes load current feedforward and thus improves the transient response with a wide load range. Secondly, an SCE strategy is proposed to enlarge the output current range and output voltage slew rate, both of which have limited value under conventional digital pulse width modulation (DPWM). When the output current reaches the limited value, the proposed strategy increases the switching cycle to enlarge the current range without losing DCM operation. Finally, combining DVP with SCE, the converter not only achieves optimal response in large signal transients, but also doubles the load range in DCM operation.

This article presents an optimal duty ratio assisted pulse frequency modulation control for very high frequency isolated class E dc–dc converter to achieve both continuous power flow and optimal switch timing. The continuous power flow significantly reduces output ripple of the converter, while the optimal switch timing guarantees consistent zero-voltage-switching (ZVS) and minimized reverse conduction loss. To pave the way for the proposed control, a resonant fitting model is established for deriving the optimal duty ratio and output power under dynamic switching frequency. The optimal duty ratio is calculated according to zero-crossing points of the switching node voltage ( v_ds ), and it aims to turn on the power switch once v_ds reaches zero. This ensures consistent ZVS while preventing reverse conduction of gallium nitride (GaN) high electron mobility transistor (HEMT) when the switching frequency changes. Furthermore, the proposed control is integrated with on/off modulation to extend load range of the converter. A 10–18 MHz prototype is built to verify effectiveness of the proposed control. Compared with conventional PFM control, the proposed control reduces the power loss by 35.9% at 40% load while maintains continuous power flow.

The permanent magnet synchronous motor (PMSM) has been widely used in the field of ship electric propulsion due to its advantages of a small size, light weight, low loss, and high efficiency. In this paper, a 100 kW ship-side thruster motor was taken as the research object, and the problem of the high harmonic content of the air gap magnetic flux density in the motor was addressed by designing a rotor eccentricity. On this basis, the hybrid Taguchi method of genetic algorithm was used to optimize the rotor structural parameters with increasing the efficiency and reducting the cost of the motor as the optimization objectives. The results show that the performance and economy of the motor have been greatly improved after optimization. Finally, the motor weight reduction hole was designed, and a prototype was manufactured and tested. The test data are within the allowable range compared with the simulation data, verifying the effectiveness of the multiobjective optimization algorithm proposed in this paper.

This paper presents a triple-mode average current control (TACC) strategy to achieve unity power factor and reduce the current stress for a boost PFC converter. The controller switches among different modes in each half-line cycle, and smooth transition is ensured by mapping of the operation region. By adaptive mode shifting, it reduces the current stress and current distortion caused by non-linear effects. With valley current shaping and comparisons, the TACC controller accordingly incorporates three control laws to adapt different modes. In discontinuous conduction mode (DCM), a variable on-time is calculated while the modulation is equivalent to PWM. In critical conduction mode (CRM), a constant on-time is derived, while the switching cycle is modified to regulate the current average value. For both DCM and CRM, the switching cycle is slightly extended to realize valley switching. Furthermore, with valley current shaping, the proposed controller reuses the CRM calculation to form continuous conduction mode (CCM) control law. To make the control laws compatible, normalized mapping and design rules are provided with respect to mode boundaries. This allows the TACC controller to automatically switch among different modes. Finally, experimental results prove the effectiveness of the controller in reducing the current stress and enlarging the preferable power range.

For very high frequency (VHF) class 2 inverter, conventional design method requires complex tuning for parameters. Without fully quantitative calculations, the tuning highly depends on experience that cannot achieve optimal design. In this paper, a target function design strategy is proposed based on quantitative harmonic weighting, which simplifies the design procedures and minimizes the switch voltage stress. Firstly, the target switch voltage with minimized peak value is derived by optimizing the harmonic weighting. With the result, the power switch is modeled as a voltage source to simplify the calculations, where the branch currents are solved to provided fully quantitative analysis. Based on the analysis, optimal features of switching node impedance are derived to achieve the target switch voltage. Additionally, basic constrains of the resonant tank are analyzed to reduce circling currents. Combining the optimal features and basic constrains of the resonant tank, the circuit parameters are calculated directly, which minimizes the switch voltage stress and improves power efficiency. Compared with conventional design, a 27.12MHz prototype demonstrates 10.2% reduction in average switch voltage stress and 7.2% improvement in average efficiency.

Nonideal switching characteristics of voltage source inverter (VSI) will result in distortions in both phase currents and reference voltages of a permanent magnet synchronous machine (PMSM) drive system, which will also consequently introduce ripples into the output speed and shaft torque, and result in a performance deterioration in the state observation control. To solve this issue, a method of directly extracting and compensating the nonlinear voltage disturbance due to VSI nonlinearity employed in PMSM drives is proposed in this paper. Firstly, the distorted voltage due to VSI nonlinearity is directly extracted via a harmonic separation scheme, which can be easily compensated by a proportional integral controller afterwards. Since both 6th harmonic and DC terms of dq -axis distorted voltages due to VSI nonlinearity are well compensated, the proposed method shows sufficiently good performance under both $i_{d}=0$ and maximum torque per ampere controls ( $i_{d} < 0$ ), as verified on two prototype PMSMs being salient pole and non-salient pole, respectively, both developed for a low-speed rotary actuator. In addition, the application of proposed method to state observation controls such as the model-based sensorless control and the deadbeat predictive current control, is finally investigated. Test results manifest that the proposed method can effectively improve the accuracy of observed rotor position/speed, and the ability of current tracking.