Relatively high torque ripple limits the further development of the switched reluctance machine, and the application of the ripple suppression method will reduce the efficiency of the system. To simultaneously improve the efficiency and torque ripple of the switched reluctance machine, a new commutation and online optimization strategy is proposed. According to the torque per ampere characteristics of the machine, two rotor position angles are defined, which are the boundaries for the high and low torque per ampere operation modes of the two adjacent phases, respectively, and for different operating modes, specific torque hysteresis control schemes are performed. Furthermore, an objective function is constructed with the efficiency and torque ripple coefficient, and during the operation of the machine, the defined boundary angles are online optimized by the genetic algorithm to maximize the value of the objective function. The effectiveness of the method is verified by detailed simulation and experiment under different operating conditions.

According to the modular power converter, a novel phase current reconstruction method using single dc-link current sensor is proposed for 3-phase switched reluctance machine (SRM), and the control method is implemented with the reconstructed phase current as well. A highly integrated modular power converter is constructed by a 3-phase full bridge and a dual switch module. The phase windings are in star-connection, and the bipolar phase currents are applied. Based on the special operating modes and single PWM signal injection, the dc-link current is decoupled and the phase current in both magnetization and demagnetization regions is reconstructed, which is very critical for the implementation of some advanced methods that require complete period phase current. The conventional control methods of the SRM, such as single-pulse voltage (SPV) and hysteresis current control (HCC) method, are carried out under different operating conditions with both simulation and experiment to verify the effectiveness of the proposed method, and the reconstruction errors and performance influences are detailed analyzed as well.

Distributed renewable energy systems play an increasing role in today’s energy paradigm. Thus, intensive research activities have been centered on improving the performance of renewable energy systems, including photovoltaic (PV) systems, which should be of multiple-functionality. That is, the PV systems should be more intelligent in the consideration of grid stability, reliability, and fault protection. Therefore, in this paper, the performance of single-phase grid-connected PV systems under an extreme grid fault (i.e., when the grid voltage dips to zero) is explored. It has been revealed that combining a fast and accurate synchronization mechanism with appropriate control strategies for the zero-voltage ride-through (ZVRT) operation is mandatory. Accordingly, the representative synchronization techniques (i.e., the phase-locked loop (PLL) methods) in the ZVRT operation are compared in terms of detection precision and dynamic response. It shows that the second-order generalized integrator (SOGI-PLL) is a promising solution for single-phase systems in the case of fault ride-through. A control strategy by modifying the SOGI-PLL scheme is then introduced to single-phase grid-connected PV systems for ZVRT operation. Simulations are performed to verify the discussions. The results have demonstrated that the proposed method can help single-phase PV systems to temporarily ride through zero-voltage faults with good dynamics.

The complex-coefficient filter-based phase-locked loop is widely used in state estimation for the constant frequency grid system. However, its performance under power systems with a variable frequency is generally unacceptable and related applications are consequently rare. This letter proposes an adaptive enhanced complex-coefficient filter-based phase-locked loop (AECCF-PLL) that accurately estimates the operational state of variable frequency grids. By deriving the relationship between model parameters and frequency, a frequency adaptive module is established to dynamically correct the model parameters in real time. Furthermore, a stability analysis of the system is provided to meet the requirements of stability and fast response for state estimation in more electric aircraft variable frequency grids and the computational workload is relatively small. Experimental tests show strong evidence for the effectiveness and validity of the proposed AECCF-PLL method.

The rotating high frequency voltage injection (RHFVI) method is widely used for sensorless control of permanent magnet synchronous motor (PMSM) at low and zero speed. The advantage of this method is that parameters tuning is easy and the convergence is good. However, the accuracy of rotor position estimation is degraded due to time delay in the high frequency (HF) current demodulation process, especially with the increasing of the rotor speed. Aimed at this issue, dual heterodyne method based RHFVI strategy is proposed to improve the sensorless performance of PMSM in this paper. Compared with the conventional method, the HF voltage is still injected into the stationary reference frame, however, the rotor position is obtained based on the HF current in the estimated synchronous rotating reference frame. Both the positive and negative sequence component of the HF current are utilized for rotor position estimation by the dual heterodyne method. Position error due to the time delay is compensated and the accuracy of rotor position estimation is improved. In the experimental part, one PMSM is tested to verify the effectiveness of the proposed method.