Guanguan Zhang

Topology and Modulation Scheme of a Three-Level Third-Harmonic Injection Indirect Matrix Converter

The matrix converter is a direct ac–ac power conversion topology. To improve the output waveform quality of the conventional matrix converter and overcome the drawbacks of the neutral-point clamped matrix converters such as the neutral-point voltage balancing issue, the limited control range of the input reactive power and the need for strict synchronization in the modulations of the rectification and inversion stages, a three-level third-harmonic injection indirect matrix converter, and a neutral-point voltage balancing algorithm are proposed. The topology consists of a line-commutated input voltage selector, a three-level inverter and a third-harmonic injection circuit, where the split dc source voltage of the inverter is formed by two input line–line voltages. Furthermore, by adopting the active power filtering technique and utilizing the third-harmonic injection circuit to compensate the neutral-point current, the neutral-point potential is balanced without extra control effort. In addition, except the advantages such as bidirectional power flow, sinusoidal input–output currents, and multilevel output voltages, the synchronization in modulations is eliminated, and the control range of the input reactive power is extended significantly. Finally, the functionality and effectiveness of the proposed methods are verified by simulations and experimental results.

A Predictive-Control-Based Over-Modulation Method for Conventional Matrix Converters

To increase the voltage transfer ratio of the matrix converter and improve the input/output current performance simultaneously, an over-modulation method based on predictive control is proposed in this paper, where the weighting factor is selected by an automatic adjusting mechanism, which is able to further enhance the system performance promptly. This method has advantages like the maximum voltage transfer ratio can reach 0.987 in the experiments; the total harmonic distortion of the input and output current are reduced, and the losses in the matrix converter are decreased. Moreover, the specific implementation of the proposed approach is developed in detail. Simulations and experiments verify the effectiveness of the proposed method.

A Robust Control Scheme Based on ISMC for the Brushless Doubly Fed Induction Machine

The brushless doubly fed induction machine (BDFM) has great potential in the wind energy generation system because it offers the advantages of higher reliability and maintenance-free operation. In this paper, a mathematical model in the power windings stator flux orientation frame is discussed by taking the rotor flux as the disturbance. Consequently, the control of the BDFM system is implemented by generating suitable control winding currents. Moreover, in order to eliminate the speed error and compensate the system uncertainties caused by the rotor flux and parameter perturbations, an integral sliding mode variable structure controller for the rotor speed is developed, and the reactive power is adjusted by a proportional-integral (PI) controller in the outer-loop. Furthermore, the control winding currents are regulated by the PI control scheme in the inner-loop. The proposed control frame achieves a good static and satisfactory dynamic control performance. Finally, simulation and experimental results are used to verify the correctness and feasibility of the proposed method.

A modulated model predictive control scheme for the brushless doubly-fed induction machine

Brushless doubly fed induction machines (BDFIMs) feature some important advantages, such as high reliability and low maintenance cost, over alternative solutions for brushless machine applications. This paper proposes a modulated model predictive control (MPC) algorithm for BDFIMs, which achieves a fixed switching frequency and superior system performance. An improvement of power quality is shown in this paper when compared to the conventional finite-control set-MPC. This paper examines the design and implementation of the modulation technique as well as presenting the simulation and experimental results to verify the technique’s operation.

Stator-current-based MRAS observer for the sensorless control of the brushless doubly-fed induction machine

Brushless doubly-fed induction machines attract much attention, but the sensorless control method have rarely discussed so far. In this paper, a sensorless control scheme of brushless doubly-fed induction machines is developed based on a simplified mathematical model. The proposed scheme is achieved by designing a model reference adaptive system observer on the basis of the control winding stator current, and a rotor speed estimator is designed by a phase locked loop. In this method, the estimated rotor speed tracks the reference value with satisfactory steady performance and a dynamic tracking response. Moreover, the estimated rotor speed is consistent with the measured value. Experimental results verify the correctness of the proposed method.

Fundamental-frequency and load-varying thermal cycles effects on lifetime estimation of DFIG power converter

Abstract In respect to a Doubly-Fed Induction Generator (DFIG) system, its corresponding time scale varies from microsecond level of power semiconductor switching to second level of the mechanical response. In order to map annual thermal profile of the power semiconductors, different approaches have been adopted to handle the fundamental-frequency thermal cycles and load-varying thermal cycles. Their effects on lifetime estimation of the power device in the Back-to-Back (BTB) power converter are evaluated.