Dazhi Wang

Performance Improvement of Quasi-Type-1 PLL by using a Complex Notch Filter

The synchronous reference frame phase-locked loop (SRF-PLL) is widely used for synchronization applications. However, it suffers from a poor performance under unbalanced and distorted grid conditions. To improve the filtering capability of SRF-PLL, moving average filter (MAF) is incorporated into its control loop at the cost of a slow transient response of PLL in recently published literature. To further improve their dynamic performance without compromising the disturbance rejection capability and stability, a novel PLL based on quasi-type-1 PLL structure is proposed in this paper. A complex notch filter is incorporated into the QT1-PLL to eliminate the fundamental frequency negative sequence voltage component. The window length of MAF in QT1-PLL is reduced. And MAF is responsible for rejecting the rest of harmonics. Parameter design guidelines are suggested to obtain the minimum settling time for both phase jump and frequency jump. The proposed PLL provides a faster transient response with higher stability margins. The effectiveness of the proposed PLL is confirmed through simulation and experimental results and comparison with advanced PLLs.

Duty Ratio Modulation Strategy to Minimize Torque and Flux Linkage Ripples in IPMSM DTC Systems

The active vector effects on torque and flux linkage are different in interior permanent magnet synchronous motor (IPMSM) systems at different times under direct torque control (DTC). These different effects may cause overcompensation or undercompensation to torque and flux linkage leading to large torque and flux linkage ripples in the IPMSM DTC systems. A novel duty ratio modulation strategy for the IPMSM DTC systems is presented, which considers these differences that are ignored in conventional duty ratio modulation strategies. The proposed duty ratio modulation strategy aims at minimizing torque ripple and flux linkage ripple, which makes sure that the control system can work in an optimum state. The active angle, the impact angle, the active factor, and the impact factor are first introduced. The active angel and the impact angle are used to get the active factor and the impact factor, respectively. Every sector is divided into five small sectors based on the impact angels, and then, a switching table is redesigned according to the small sectors division. Also, the vector selection rules for the redesigned switching table are described in details. Subsequently, an optimal duty ratio can be derived through the simplified duty ratio determination method. Finally, the effectiveness of the proposed novel modulation strategy is verified through the experimental results on a 100-W IPMSM drive system.

An Evolutionary Algorithm for the Texture Analysis of Cubic System Materials Derived by the Maximum Entropy Principle

Based on the principle of maximum entropy method (MEM) for quantitative texture analysis, the differential evolution (DE) algorithm was effectively introduced. Using a DE-optimized algorithm with a faster but more stable convergence rate of iteration reliable complete orientation distributions (C-ODF) have been obtained for deep-drawn IF steel sheets and the recrystallized aluminum foils after cold-rolling, which are designated as showing a macroscopic cubic-orthogonal symmetry. With special reference to the data processing, no more other assumptions are required for DE-optimized MEM except that the system entropy approach the maximum.

Sensorless Control of PMSM Based on Sliding Mode Observer

A novel sliding mode observer(SMO) of PMSM(permanent magnetic synchronous motor) was presented, which estimated the rotor position and angular velocity accurately.The proposed SMO substitutes a sigmoid function for the conventional signum function with a variable boundary layer which is changed according to the rotational velocity.The dependence to motor parameters and chattering effects that is commonly found in signum function using for the switching function were overcome.By combining the model of PMSM under d-q coordinate,the convergence condition of observer was deduced.The convergence was verified by the Lyapunov theory.Simulation results show that the rotor position and velocity can be observed accurately,and also has good dynamic performance and robustness.

An Improved Harmonic Current Detection Method Based on Variable Forgetting Factor RLS Algorithm

The effects of compensating and restraining the power system harmonics using active power filter are determined by the detection precision and its dynamic response characters. To improve both of them, a harmonic current detection algorithm based on variable forgetting factor Recursive Least-Squares algorithm is presented. The occurrence of the dynamic process is identified firstly by the judgment condition which is given by the algorithm, and then the forgetting factor is assigned dynamically, so that the convergent speed is significantly improved. The algorithm overcomes the impact of low-pass filter of traditional p-q or ip-iq algorithm, and releases the contradiction cased by the conflicting requirements of forgetting factor value between steady process and dynamic process. So it has better dynamic performance. Simulation and experiments prove the validity and feasibility of the approaches.

Quantitative Determination on Fiber Textured Materials Derived by Particle Swarm Optimization

In this article presented, the maximum entropy method (MEM) assisted by the particle swarm optimization (PSO) algorithm with inertia weight factor was adopted to quantify the volume percentage of crystalline grains corresponding to the {100} fiber texture in high-purity Aluminum foils. The results derived from the inverse pole figures indicate a simpler and more convenient method than the ones derived by the conventional metallographic analysis in comparison, which possess a relative error less than 5% in general. In consideration of the measurement error relating to the metallographic method, this improved quantification is more accurate and acceptable.

An Improved ODF Representation on Textured Materials Derived by Particle Swarm Optimization

Based on the principle of maximum entropy method (MEM), the particle swarm optimization (PSO) with inertia weight factor is efficiently applied for the orientation distribution function (ODF) representation on textured materials in this article. By this optimized algorithm with a faster rate of convergence, more appreciable calculation results have been obtained for complete orientation distributions (C-ODF) of the designated deep-drawing IF steel sheets with macro cubic-orthogonal symmetry. With reference to data processing, there need no more assumptions except that the system entropy approaches maximum. The calculation results are irrelevant to the sample compositions, texture components or their initial orientation distributions derived from three pole figures.