Yuwen Hu

Wide-Speed-Range-Operation Dual Stator-Winding Induction Generator DC Generating System for Wind Power Applications

This paper presents a wide-speed-range-operation dual stator-winding induction generator (DWIG) dc generating system for wind power applications. In this system, the dc bus on the control-winding side and the dc bus on the power-winding side are connected in parallel to further widen the speed range of the constant dc voltage output, especially at low speeds. Based on the control mechanism of the DWIG and the instantaneous power theory, a control-winding-flux-orientation control strategy is employed. In order to improve the wind energy conversion efficiency at low wind speeds, the generator efficiency optimization method is investigated. The experimental results from a 20 kW/600 V prototype show that the proposed generating system can output the constant dc voltage in a speed range of 1:4, and the generator efficiency in the low speed range is improved, which both bring the advantages for wind power applications, such as expanding the scope of the wind energy utilization and capturing much more wind energy.

A fast algorithm for SVPWM in three phase power factor correction application

A novel algorithm for space vector pulse width modulation in three phase power factor correction applications is proposed. The durations for the active vectors that formed the sector containing the desired reference voltage vector are calculated directly by matrix pre-decomposing, without looking up sinusoidal and tangential tables, based on TMS320F240. Therefore running speed and control precise of the program can be improved greatly. As a result the switching frequency and power density of the rectifier is increased considerably. A new method for detecting sector is given as well. Simulated and experimental results are provided to verify the proposed algorithm in the end of the paper.

Low cost compound current sharing control for inverters in parallel operation

A compound control scheme for inverters in parallel operation is proposed. The synchronization control is decoupled from current sharing control by local feedback. In each inverter module, the sinusoidal reference of output voltage is generated in digital manner, the phase angle of which is determined by a sharing synchronous square-wave signal. Based on average method, the current sharing is realized through simple analog circuits. The amplitude of the reference voltage is also regulated according to the circulating current to improve load balance performance. All the control circuits for parallel operation, sharing a digital synchronous signal and an analog current reference, are equally distributed in the modules. Theoretical analysis and experimental results are presented to demonstrate the performance of the proposed control scheme of parallel operation.

A novel direct torque control for electrically excited synchronous motor drives with high power factor and low ripples in flux and torque

A direct torque control (DTC) method for electrically excited synchronous motor (ESM) drives has been investigated in this paper. It is based on the compensation of the stator flux linkage vector error using the space vector modulation to decrease the ripples in torque and flux linkage. In order to increase the power factor and load ability of ESMs, an optimum rotor field current control scheme has been presented, which is suited well in the whole speed range. In the closed loop of the rotor current control, the reference rotor current is directly calculated with the torque and stator flux linkage modulus references. Compared to the traditional DTC method, the results of experiments show that the presented DTC has low ripples in torque and flux linkage, and almost achieves unity power factor.

Analysis, Comparison, and Discussion of Control Strategies for Dual Stator-Winding Induction Generator DC Generating System

This paper presents four types of control strategies for a dual stator-winding induction generator DC generating system as well as their analysis, comparison, and discussion. These four types of control strategies include control-winding flux orientation control, control-winding voltage orientation control, control-winding direct power control, and instantaneous slip frequency control (ISFC). The ISFC strategy is described in detail for first employed in dc generating application, and the other strategies are briefly introduced and their performances are also summarized for comparison. The characteristics of control strategies are compared from four aspects: 1) system performance; 2) key components; 3) control principles; and 4) applications. From the comparison results, it can be inferred that all these four types of control strategies have some advantages, especially the ISFC. They can find suitable applications.

Research on Three-Phase High Power Factor Correction Based on Predictive Current Controller

A predictive current controller applied in a three-phase PWM rectifier is proposed. It can simplify the design of the current control loop and occupies less memory and interrupt resource in the DSP (digital signal processor). Together with the decomposition-matrix method, the total algorithm can be completed only with one timer and its underflow interrupt subroutine. The predictive current controller helps to design the voltage regulator and make the input currents track the input voltages so well that high power factor can be achieved. Finally the experimental results are given to verify the proposed predictive current controller.

Control and Performance of Five-Phase Dual Stator-Winding Induction Generator DC Generating System

In this paper, the five-phase dual stator-winding induction generator dc generating system with the static excitation controller is presented, and two kinds of control strategies for this system are proposed. In this generator, the cage-type rotor is employed, and two sets of five-phase windings are placed in the stator, namely, the power winding and control winding. Using the instantaneous power theory, the control-winding-flux-oriented control (CWFOC) strategy without harmonic injection is obtained. To improve power density, the CWFOC with harmonic injection is proposed as well. For these two strategies, the detailed implementation is studied. The results (simulation and experiment) support the correctness and effectiveness of the proposed control strategies, and the corresponding results show that, using the CWFOC strategy with harmonic injection, the output power of this system can be improved by about 11%.

Asymmetrical Operation Analysis for Dual Stator-Winding Induction Generator Variable Frequency AC Generating System With Unbalanced Loads

In this paper, the performance of the dual stator-winding induction generator (DWIG) variable frequency ac (VFAC) generating system with unbalanced loads is analyzed, and an asymmetrical operation analysis method based on a three-port load network model is proposed. This method has four key steps: (1) deriving the three-port load network model for three-phase four-line unbalanced loads; (2) establishing the positive sequence, negative sequence, and zero sequence equivalent circuits for the DWIG; (3) combining the above model and circuits together to obtain the system whole equivalent model; and (4) writing the corresponding equations and solving them. The experimental results and the calculation results are almost consistent, which proves that the proposed method is correct and valid, and the DWIG VFAC generating system with unbalanced loads has a good performance.

An instantaneous slip frequency control strategy for the dual stator-winding induction generator variable frequency AC power system

This paper presents an instantaneous slip frequency control (ISFC) strategy for the dual stator-winding induction generator (DWIG) variable frequency AC (VFAC) power system. In this ISFC scheme, the information of both the output voltage and the output power is employed to guarantee the system has a desirable static and dynamic performance. The experimental results on a 15 kW prototype verify the principle and performance of the proposed control method.

Neutral-point balance based on current sensor-less hysteresis control for three-level diode-clamped PWM rectifier

The reason why the neutral point voltage fluctuates is analyzed in detail and a current-sensorless hysteresis control strategy proposed. This way to balance the neutral-point voltage is simple and not need of current sensor. Based on small signal control model and neutral-point voltage balanced technique the experimental prototype are given and the experimental results verify that the proposed mathematic is correct and the balance of neutral-point voltage guarantee high power factor of TL-PWM rectifier.