Changzhou Yu

With the rapid development of renewable energy, the widespread integration of power electronic devices into power generation systems has led to increased grid impedance and reduced short-circuit ratio (SCR), causing the grid to exhibit characteristics of weak or even extremely weak grids. This has posed significant challenges to traditional grid-following control strategies, resulting in increased grid harmonics, heightened instability risks, and frequent power generation system failures. In contrast, grid-forming control strategies, which provide active voltage support, have demonstrated superior stability in weak grid conditions. However, neither grid-following nor grid-forming control strategies alone can comprehensively meet the requirements of power systems in terms of stability, economic efficiency, and grid support. To address these challenges, this paper proposes a model predictive control (MPC) strategy that integrates grid-following and grid-forming control. First, a mathematical model of the grid-connected inverter is established, and stability analyses are conducted for both grid-following and grid-forming modes. Second, model predictive control algorithms are thoroughly investigated for both modes, and an optimized control strategy is selected through comparative analysis. Finally, the effectiveness of the proposed strategy is validated using a hardware-in-the-loop (HIL) simulation platform. Experimental results demonstrate that the proposed method significantly enhances the stability of grid-connected inverters under conditions of significantly increased grid impedance and reduced SCR, ensuring reliable operation of power systems. This approach holds substantial practical application value for modern power systems.

The doubly salient electromagnetic machine (DSEM) has broad application prospects in fields such as electric vehicles and aviation, which puts higher requirements on its reliability. Fault-tolerant control is one of the effective ways to improve the reliability of the DSEM. At present, there are few studies on fault-tolerant control when excitation faults occur. This article proposes a fault-tolerant control strategy based on the current profile function for the DSEM drive systems with excitation faults. First, the current commutation process is optimized to suppress torque ripple based on the torque and current variation characteristics of the DSEM under loss of excitation. Then, the distribution ratio of the three-phase currents that minimize the instantaneous copper loss of the armature windings is derived for the current noncommutation process. On this basis, a three-phase current profile function is designed, which is combined with torque closed-loop control to reduce torque ripple. Finally, the experiments on an 18/12 pole DSEM system are performed to validate the effectiveness of the proposed fault-tolerant control method, which can reduce the torque ripple and improve the torque–ampere ratio.

The inductance parameter is crucial to realize high-precision model predictive control (MPC) for grid-connected inverter (GCI), while the traditional inductance estimation method is sensitive to the grid frequency deviation and cannot work normally when the active power is zero. To solve these problems, a new inductance online estimation method based on a full order sliding mode voltage observer (FSMVO) is proposed. First, the drawbacks of the traditional FSMVO-based inductance estimation method are analyzed. Second, a new inductance estimation method is proposed, which uses the error between the observed grid voltage and the actual one passed through a filter, whose transfer function is the same as the one of FSMVO. As a result, the new inductance estimation method is immune to the grid frequency deviation. Moreover, a new Lyapunov function is also designed in this article to deduce the new inductance estimation method, which can work well, no matter the active power is zero or not. Finally, by substituting the estimated inductance parameter into the MPC algorithm, the control performance of GCI can be improved. The effectiveness and accuracy of the proposed inductance estimation method are verified by experimental researches.

Silicon carbide (SiC) MOSFETs are garnering widespread attention due to their superior performance in high‐temperature, high‐frequency, and high‐voltage applications, emerging as the preferred power semiconductor devices in converters for photovoltaic power generation and new energy vehicles. However, SiC MOSFETs are prone to gate drive and drain‐source voltage oscillations during high‐speed switching events, resulting in diminished system efficiency, increased electromagnetic interference, reduced device safety, and even compromising the overall reliability of the converter. This paper introduces an oscillation suppression method based on a gate LCR parallel branch, aimed at optimizing the switching performance of SiC MOSFETs. A half‐bridge circuit model based on SiC MOSFET is established, and the mechanism of gate and drain‐source oscillation is meticulously analysed using the transfer function expression. Building upon this, the LCR parallel branch parameters are meticulously designed to introduce appropriate damping in the gate drive path, effectively mitigating oscillations. Experimental results demonstrate that the proposed design not only significantly reduces the amplitude of oscillations but also shortens the switch‐transition time. This enhancement effectively increases the switching frequency and reduces switching losses.

A magnetic component parameter design method is studied to optimize current stress in dual active bridge (DAB) DC-DC converters, which can cause a sharp increase in current stress when voltage mismatch occurs, leading to increased switching device losses and reduced switching device lifespan. Firstly, after considering the factors that affect current stress, a mathematical model of current stress is constructed. Secondly, combined with single phase shift control, a three-dimensional surface map of current stress is constructed, which can intuitively reflect the corresponding current stress under different magnetic component parameters, making it easy to quickly select and optimize the magnetic component parameters under current stress. Finally, an experimental platform for the dual active bridge DC-DC converter was built, and the correctness and feasibility of the design scheme were verified through experiments.

Aiming at the problems of slow response speed of the output active power of the new energy converter based on droop control, and large active power oscillation and overshoot in the dynamic process, a new energy converter control method based on the drop of the hyperbolic tangent function is proposed. This method first calculates the average value of the output active and reactive power of the converter; then performs the hyperbolic tangent function droop control on the active power to obtain the angular frequency command of the output voltage; performs linear droop control on the reactive power to obtain the output voltage Amplitude command; finally, double closed-loop control of output voltage and inductor current in dq coordinate system. Compared with the traditional droop control, the simulation results show that the output active power response speed becomes faster, and it has a shorter dynamic adjustment process.

To support the “carbon peak and carbon neutrality” goal, new energy is poised to explode, and new energy power generation converter is simultaneously facing new challenges. The conventional current-controlled new energy converter can quickly transmit active power on the DC bus to the power grid. However, for the weak grid, the stability margin of the converter grid-connected system is reduced on the one hand, which can easily cause resonance oscillation; on the other hand, the current controlled converter cannot actively respond to system frequency and voltage fluctuation to offer support. The voltage controlled virtual synchronous generator (VVSG) is used to improve system small signal stability and frequency stability; however, its power response speed is too slow to meet the requirements of fast following power command. Although a voltage/current dual-mode switching control scheme is put forward to achieve characteristics complementary of current controlled converter and voltage-controlled converter, the control structure switching and intermediate variable following is required to realize mode switching, which is prone to large power shocks and switching failures. In view of the problem, a direct power control strategy based on VVSG is proposed. The control structure is raised based on a conventional VVSG outer active power control loop, and the output active power and frequency characteristics are analyzed. Compared with the voltage and current dual-mode control, VVSG with direct power control can perform large inertia characteristic in the weak grid and fast power following characteristics in the strong grid by adjusting λ, and without control structure switching and intermediate variable following. Moreover, the two characteristics can be smoothly transited. In addition, the active support ability of voltage source can be maintained under both characteristics. Finally, the effectiveness of the proposed control strategy is verified through simulation results.