In order to solve the imminent problem in that the traditional protection strategy cannot meet time requirements, together with the fact that the rotational inertia of a DC microgrid is small and short-circuit fault develops rapidly, a bidirectional short-circuit current blocker (BSCCB) based on solid-state circuit breaker for a DC microgrid is proposed. Firstly, the bidirectional current blocking circuit structure is proposed based on the analysis of key components. Then, a top-level differential protection strategy is developed based on the aforementioned proposal. Finally, the performance of the blocking circuit is simulated and verified by experiments. The results show that the proposed method can block short-circuit current within 4 ms, and the response speed of the protection strategy is very fast compared with previous approaches. BSCCB also has reclosing, bidirectional blocking and energy releasing functions. The current blocker proposed in this paper can be reused multiple times and has a promising future in low-voltage DC microgrid application.

with the widespread growth in the use of electric vehicles (EVs), there is an urgent demand for fast-charging battery charger so as to alleviate the range anxiety for car users. A novel multi-pulse flexible-topology thyristor-based rectifier (mPFTTR) is proposed in this paper, which can be a suitable candidate for high-power fast-charging battery charger of the EVs. The proposed architecture has five operating modes: series mode with 24 pulses (SM24P), parallel mode with 24 pulse (PM24P), hybrid modes with 24 pulses (HM24P), series mode with 12 pulses (SM12P) and parallel mode with 12 pulses (PM12P). To meet the practical requirement of fast charging, the predictive current control strategy combined with multi-step constant current charging (MSCCC) is also proposed, and followed by the detailed implementation and analysis. Simulation and experimental verifications are carried out, and both results show that the predictive current control strategy combined with the MSCCC method can charge the EVs with wide-range input voltage, and fast charging is also achieved. Finally, efficiency evaluation and comparisons of total harmonic distortions (THDs) of the input current are developed between the proposed mPFTTR which operates in HM24P and the conventional thyristor-based rectifier which operates in SM24P.

In order to solve the excitation problem of elevator traction permanent magnet synchronous motors (PMSMs), a new high-order sliding mode flux observer based on a hybrid reaching rate is proposed under the background of industrial engineering to detect loss of excitation faults in real time. Firstly, a new high-order sliding mode flux observer is designed to solve the problem of the traditional sliding mode observer not being able to accurately detect the loss of excitation fault when the load resistance changes. Then, based on the sliding mode variable structure equivalent control principle, a PMSM flux estimation formula is established. The sinusoidal input function replaces the traditional symbolic process, and a mixed approach law is designed to replace the constant speed approach rate. The adaptive adjustment of the boundary layer of the sinusoidal input function is realized through a fuzzy control system, which effectively suppresses the chattering problem caused by the sliding mode variable structure and improves the observation accuracy of rotor position. The stability of the system is verified by Lyapunov’s second method. MATLAB/Simulink is used to build the simulation model of the PMSM control system with the new sliding mode observer, and the simulation results are compared with those of a traditional sliding mode observer. The results show that compared with the conventional observer, the new sliding mode observer can track the rotor position quickly, and the system has better anti-interference abilities and stability. Finally, the feasibility and effectiveness of this method are verified via simulations and experiments.

This paper proposes a new variable-mode control strategy that is applicable for LLC resonant converters operating in a wide input voltage range. This control strategy incorporates advantages from full-bridge LLC resonant converters, half-bridge LLC resonant converters, variable-frequency control mode, and phase-shift control mode. Under this control strategy, different input voltages determine the different operating modes of the circuit. When the input voltage is very low, it works in a full-bridge circuit and variable frequency mode (FB_VF mode). When the input voltage rises to a certain level, it shifts to a full-bridge circuit and phase-shifting control mode (FB_PS mode). When the input voltage further increases, it shifts into a half-bridge circuit and variable frequency mode (HB_VF mode). Such shifts are enabled by the digital signal processor (DSP), which means that no auxiliary circuit is needed, just a modification of the software. From light load to heavy load, the primary MOSFET for the LLC resonant converter can realize zero-voltage switching (ZVS), and the secondary rectifier diode can realize zero-current switching (ZCS). With an LLC resonant converter prototype with a 300 W rated power and a 450 V output voltage, as well as a resonant converter with 20–120 V input voltage, the experiments verified the proposed control strategy. Experimental results showed that under this control strategy, the maximum converter efficiency reaches 95.7% and the range of the input voltage expands threefold.

High pressure sodium (HPS) lamp has been widely used in street lighting applications because of its maturity, reliability, high lighting efficiency, long l