An improved high-frequency pulsed sinusoidal voltage signal injection (HFPS-VSI) sensorless control strategy applied to interior permanent magnet synchronous motor (IPMSM) is proposed in this paper. In the high-frequency (HF) current signal demodulation process, this paper proposes a demodulation approach that can demodulate a four times injection frequency component. Hence, a low-pass filter (LPF) with higher cut-off frequency can be selected to suppress the HF component. The proposed demodulation method can improve the bandwidth of the position estimation loop and increase the signal-to-noise ratio (SNR) of position angle errors fed to the rotor position observer. To enhance the current loop bandwidth, this paper utilizes the current observer (CO) to extract the fundamental current. Theoretical analysis shows that the proposed fundamental current extraction method has no amplitude attenuation and time delay, and is robust against motor parameter mismatches at the fundamental frequency. Therefore, it can eliminate the LPF used in the fundamental current extraction to improve the dynamic response of the current loop. Meanwhile, a design method of CO is proposed, which makes CO keep a constant and high bandwidth in the low-speed region, suited for low-speed sensorless operation. Finally, the effectiveness of the improved HFPS-VSI algorithm is verified by experimental tests.

The encoderless deadbeat predictive current control (DBPCC) has been widely applied in surface-mounted permanent magnet synchronous motor (SPMSM). However, the DBPCC suffers from poor performance against motor parameters mismatches. An improved encoderless DBPCC method with online parameter identification is proposed to enhance the parameter robustness in this article. Firstly, a modified rotor position estimator is directly designed in the discrete-time domain. No observer is required to estimate back electromotive force (EMF). Hence, the proposed EMF estimator features simple structure and easy implementation. Then, the parameter sensitivity of the encoderless DBPCC method is analyzed. A simple demodulation method is proposed to identify motor parameters based on the injected high frequency current signals in the d -axis. The proposed online parameter identification algorithm would not introduce the extra torque harmonics in SPMSM. Meanwhile, theoretical analysis shows that the proposed parameter identification method presents high precision even with the severe initial motor parameters mismatches. Therefore, the mismatched parameters used in the encoderless DBPCC method can be replaced by the identified motor parameters to precisely correct the rotor position estimation errors. Finally, the experiments were tested in a two-level inverter-fed SPMSM drives to validate the effectiveness of the proposed encoderless DBPCC algorithm with online parameter identification.

Different from the voltage source inverter (VSI), the current source inverter (CSI) can boost the voltage and eliminate the additional passive filter and dead time. However, the DC-side inductor current is not a real current source and is generated by a DC voltage supply and an inductor. Under different switching states, the DC-side inductor will be charged or discharged, which leads to the DC-side inductor current being discontinuous or increasing. To solve the control problem of the DC-side inductor current of the CSI, a novel single-phase CSI topology with five switching tubes for grid-connected applications is proposed. Firstly, the reference calculation method and the hysteresis loop control scheme for the DC-side inductor current are proposed, and the adjustable and constant DC-side inductor current are obtained. Since the PWM signals cannot be directly implemented to the switching tubes, the modulation strategy for the single-phase CSI is proposed in this paper. Then, an active damping method based on the feedback capacitor voltage is presented to suppress the resonance peak caused by the LC filter on the grid side. Finally, the math model of the AC-side structure is established, and the optimal proportional-resonant controller parameters’ design method is explored by the amplitude–frequency characteristic curves. The simulation and experiment are implemented for the proposed CSI topology. The results show that a high-quality power with a good control performance can be obtained with the proposed CSI topology.

In this paper, early stage of granular materials flowing through the orifice of a cuboid hopper with flat bottom is investigated based on the results generated by using the discrete element method. The results show that in the start up stage of the flow, a switch curve is formed between static and flowing particles, and a force arch on which the forces are very small is generated below the switch curve. Both curves propagate into the granular bed with the discharge of particles, and reach the top of the bed when a steady state is achieved.