The direct torque control (DTC) technique of permanent-magnet synchronous motors (PMSMs) receives increasing attention due to its advantages in eliminating the current controllers and quicker dynamic response, compared with other motor control algorithms. However, high torque and stator flux ripples remain in the system when using DTC technologies. This means large stator voltage and current harmonic contents exist in the PM motors. Since the variation of motor electromagnetic torque is related to the voltages that are applied to the motor, by analyzing the relationships between stator flux, torque, and voltages, a PMSM torque predictive control scheme is proposed in this paper. In each digital signal processor cycle, the optimized voltage is utilized to reduce torque ripple, and the voltage vector angle is determined by the output of torque and flux hysteresis controllers. The proposed scheme is simulated and experimentally verified. Both simulation and experimental results have shown that low torque ripple and reduced stator current harmonics are achieved by using the proposed scheme.Index Terms-Permanent-magnet synchronous motor (PMSM), torque predictive control (TPC), torque ripple, voltage angle.

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We prepared La doped of CaCu3Ti4O12 ceramics by a solid-state sintering process and observed nonlinear electrical varistor and high dielectric behaviors. Phase composition analyses show that the La can substitute on the Ca sites completely, and have no influence on the phase composition. The impedance spectroscopy at room temperature indicates that the La doping can maintain the dielectric permittivity of CaCu3Ti4O12 (∼104). The relationships between electrical current density versus applied electrical field show that these ceramic samples exhibit nonlinear varistor characteristics, which should be ascribed to the existing potential barrier height at the grain boundary.

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When connected to a distorted grid utility, droop-controlled grid-connected microgrids (DCGC-MG) exhibit low equivalent impedance. The harmonic and unbalanced voltage at the point of common coupling (PCC) deteriorates the power quality of the grid-connected current (GCC) of DCGC-MG. This work proposes an active, unbalanced, and harmonic GCC suppression strategy based on hierarchical theory. The voltage error between the bus of the DCGC-MG and the grid's PCC was transformed to the dq frame. On the basis of the grid, an additional compensator, which consists of multiple resonant voltage regulators, was then added to the original secondary control to generate the negative fundamental and unbalanced harmonic voltage reference. Proportional integral and multiple resonant controllers were adopted as voltage controller at the original primary level to improve the voltage tracking performance of the inverter. Consequently, the voltage difference between the PCC and the system bus decreased. In addition, we established a system model for parameter margin and stability analyses. Finally, the simulation and experiment results from a scaled-down laboratory prototype were presented to verify the validity of the proposed control strategy. Index Terms-grid-connected current; power quality; droop; distorted; unbalance; hierarchical control. I. INTRODUCTION enewable energy has drawn considerable attention in recent years because of growing concerns regarding traditional fossil energy shortages and other environmental problems. Therefore, power systems have undergone major changes not only for ensuring sustainable development but also for solving power supply problems in remote areas [1]-[2]. One such innovation is the microgrid (MG), which can integrate different kinds of energy sources and power electronics interfaced with units of distributed generations (DGs). Over time, MGs became expected to perform even more functions and complex. Thus, an advanced MG hierarchical theory was proposed to define the system on three levels, thereby facilitating controller design depending on the different

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This paper proposed a state observer based on extended kalman filter (EKF) for the rotor speed and load torque observation of permanent magnet synchronous motor (PMSM). This observer can be used to estimate the precise rotor position and rotor speed in the servo systems with only optical encoder of limited accuracy. By using the observed rotor speed and position instead of the values got directly from the encoder, the speed and position control performances can be greatly improved. The observer can also give the load torque which can be used as the feedforward compensation of the speed PI controller. The compensation can greatly improve the speed control performance during load torque change. The extended Kalman filter is used to solve the nonlinear equation of the observer, considering the influence of the parameter errors and the noise in measurement. So it is very robust to the parameter errors.