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To reduce the common-mode voltage (CMV) as well as the current total harmonic distortions (THDs) of 2-level voltage source inverters (2L-VSIs), a hybrid single and double-voltage vector (VV)-based model predictive control (MPC) method is proposed. Firstly, a two non-zero VV-based MPC strategy is proposed to reduce the CMV as well as the current THDs. Secondly, the influences of the dead time on this method are analysed in detail, and an improved VV preselection method is further proposed to remove the dead time effects. Thirdly, considering the impacts of the control delay and the current ripples, a new current sector division method is presented, based on which a hybrid single and double-VV-based MPC strategy is finally proposed. Furthermore, the current variation per control period under the action of different VVs is also analysed in-depth in this study to lay a solid theoretical foundation for dividing the current sector more properly. Both the simulation and experimental studies are carried out to verify the effectiveness of the proposed method.

To enhance generating capacity and reliability of multi-machine parallel power generation, implement the efficiency optimization, a current distribution control method based on differential evolution (DE) algorithm is proposed for the switched reluctance generator (SRG) in parallel. The load current is stabilized by the maximum value current sharing control (CSC) firstly. Then, the current distribution control method is adopted, which can adjust the reference current of each parallel generator in the current distribution part, so as to change the working point of each generator and implement the optimization of parallel system efficiency. The performances of the proposed control method are evaluated in detail by the simulation, and comparison with traditional current sharing control is carried out as well.

For the purpose of acquiring the accurate grid impedance, a complex coefficient filter (CCF) based grid impedance identification method is studied in this paper. High frequency non-characteristic harmonic voltages and currents are injected into the power grid by the power converter firstly. Next, a CCF is used to extract these high frequency voltages and currents from the sampled voltages and currents at the point of common coupling. Then, the grid impedance is calculated based on the extracted voltages and currents. Considering that the impacts of the DC offset on the grid impedance identification cannot be removed by the conventional CCF, an improved CCF is proposed in this paper by adding a high-pass filter to the forward channel of the conventional CCF. The filter characteristic of the proposed CCF is analyzed, which shows its DC offset suppression capability. Simulation results show the effectiveness of the proposed grid impedance detection method.

Bidirectional AC/DC converter can be reconstructed as a three-phase four-switch (TPFS) fault-tolerant converter when leg fault occurs to enhance its fault tolerant operation capability. In this paper, to further improve the control performance of the TPFS fault-tolerant converter, a new model predictive control (MPC) method is proposed. Considering that there are only four voltage vectors for the TPFS fault-tolerant converter, to reduce the current ripples, double voltage vectors are selected and applied per control period in the proposed method. To reduce the calculation burden, the duration time of each voltage vector is calculated based on the principle of the modulated MPC. Furthermore, the effectiveness of the proposed double-voltage vector based MPC strategy is analyzed in theory in detail for the first time and then it is further verified by comparative simulation studies.

Sliding mode observers are often utilized to achieve the speed sensorless control of permanent magnet synchronous motors. However, due to the nonlinearity of the sampling channel, DC offset is often contained in the sampled voltages and currents of the permanent magnet synchronous motor, which may further reduce the speed sensorless control accuracy. Besides, the speed sensorless control accuracy is usually very poor due to the low signal-to-noise ratio in the low speed region. In this paper, to improve the speed sensorless control accuracy in the low speed region and remove the effects of the DC offset, a new super-twisting sliding mode observer based speed sensorless control method is proposed for permanent magnet synchronous motors. First, based on the concept of the equivalent feedback, a new super-twisting sliding mode observer is proposed. Second, the effects of the DC offset on the speed sensorless control are analyzed in detail, and a second-order generalized integrator is used to remove the DC offset contained in the observed equivalent feedback signal. Then, a phase-locked loop is used to estimate the speed and the rotor position to achieve speed sensorless control. Finally, the effectiveness of the proposed control strategy is verified by a 6.6 kW permanent magnet synchronous motor speed sensorless control system.