Xiaojie You

A new sliding-mode current controller for field oriented controlled induction motor drives

Accurate and fast current control is essential in high performance field oriented controlled induction motor drives. In this paper, a new sliding-mode current controller is presented for induction motor drives. This scheme uses two sliding-mode controllers to regulate the d-axis and q-axis stator currents respectively, and adopts space vector modulation (SVM) technique as the voltage modulation strategy. This new current controller exhibits several advantages such as fast dynamic response, perfect decoupling and robustness to parameter variations. Simulation results are provided to verify the performance of the proposed current control scheme

The grid connected converter control of multi-terminal DC system for wind farms

This paper researches the layout of the multi-terminal DC (MTDC) system consisting of several voltage source converters (VSC) in wind farms and presents the control strategy of grid-connected converter. The generator-side converters of MTDC system aggregate the power of wind turbines into a DC grid. Then a grid-side converter inverts the collected power into a three-phase AC electric utility grid. The dynamic model of three-phase VSC is developed at synchronous reference frame with grid voltage. By introducing the decoupling components in control law, the grid-connected VSC controls the DC voltage of MTDC system and the reactive power respectively. The simulation results verify the performance of the proposed method

Design Method for the LCL Filters of Three-phase Voltage Source PWM Rectifiers

A new design method for the LCL filters of three-phase voltage source PWM rectifiers is presented in this paper. Based on the single-phase harmonic equivalent model, the harmonic voltage of the rectifier side is calculated to design the LCL filter parameters by an iterative algorithm, in which the resonance frequency fres and the ratio r between the grid-side inductance and the rectifier-side inductance are selected as known constants. The design criteria and process are introduced and the influence on the design result by the value of the resonance frequency fres, ratio r is analyzed. Finally an example (600V, 500kW) is tested by simulation and experiment to verify the validity of the new design method.

Speed estimation of induction motor using modified voltage model flux estimation

Speed estimation in field-oriented vector control of induction motor depends on effective estimation of rotor flux. This paper proposes speed estimator using improved rotor flux estimator based on modified voltage model with a high orders low-pass filter (LPF) and a low-pass filter in series and an error compensator by rotor flux oriented current model. In the flux estimation based on voltage model, a high orders LPF can remove the DC offset input of Back EMF, a LPF is normally used to replace the pure integrator to avoid integration drift and saturation problems and the flux estimation error is compensated according to rotor flux oriented current model. The proposed the speed estimator realizes errorless speed estimation in steady state and makes the error of speed estimation smaller in dynamic state. The speed estimation is verified by speed sensorless field-oriented vector controlled 2.2kW induction motor. Experimental results demonstrate high performance of the speed estimator.

Power electronics used in Chinese electric locomotives

The Chinese railways are characterized by a wide range of various locomotive series. Nowadays, 80% of the locomotives driven by electricity run on the most main railroads. Most of the electric locomotives designed by AC-DC traction system till 2003 while DJ1 locomotives manufactured by AC-DC-AC traction system. Power Electronics is one of the pivotal parts of the whole locomotive equipment, playing important roles in power outputting, traction torque releasing, brake dynamic inflicting etc. This paper probes into 3 ages of the power electronics technology used in the electrical locomotives in China. The line-commutated control (thyristor and diodes) and the line-commutated control (thyristor and diodes) in traction and auxiliary system delegates the different age. Problems in system design concerning match of invert and asynchronous traction motor are discussed. Main circuit diagram, power electronics and general technical parameters are presented. At last, The paper gives a comparison of the traction characteristic for the electrical locomotive in different age.

A new single-phase to three-phase cycloconverter for low cost AC motor drives

This paper presents a new single-phase to three-phase cycloconverter suitable for driving an induction motor. Using discrete variable frequency technique, a single-phase to three-phase modulation strategy is proposed, the output frequency of this cycloconvertor can be up to half of the input frequency. Only six naturally communicated thyristors are employed, so the resulting cycloconverter-motor drive system is cheap and compact. Software in C and assembly language has been written for real-time control. The simulation based on Matlab/Simulink is used to predict the performance for the cycloconverter and induction motor.

Power quality controller based on hybrid modular multilevel converter

This paper presents a hybrid modular multilevel converter (HMMC) based power quality controller (HM-PQC) intended for medium- or high-voltage applications. HM-PQC is characterized by cascaded connection of leg inductors and power units. Modular structure makes it easily be extended to high-level, thus leading to low voltage steps and low generation of EMI problems, etc.. Comparing with the conventional star-connected cascaded H-bridge converter, HM-PQC can be controlled for improving various power quality problems in three-phase balanced or unbalanced power systems. The circuit configuration and operation principles of HMMC were presented in detail. Moreover, power quality control strategies of HM-PQC were proposed for different compensation purpose. Experimental results show that HM-PQC is suitable for comprehensive mitigating of all the power quality problems, such as reactive power compensation, harmonic suppression and negative-sequence balancing.

Power quality analysis of traction supply systems with high speed train

The characteristic of harmonic currents of high speed train is significantly different from DC-drived locomotives. The rectifier of CRH5 Electric Multiple Units (EMUs) in China is researched in this paper.The principle of four-quadrant converter and its predictive current control strategy are studied. The formula of fundamental and harmonic currents of the parallel two-level four-quadrant converter is given under different power and grid voltage based on double Fourier Transform Method. Therefore the distribution characteristics of harmonic currents are analyzed. The simulation software based on Matlab / Simulink is developed for harmonic analysis of CRH5 EMUs. With different traction power, braking power and traction grid voltage, the harmonic currents of EMUs injecting to the traction grid are studied and compared.

Nonlinear PID control for three-phase PWM rectifier based on predictive current control

This paper proposes a nonlinear PID control strategy for three-phase voltage source PWM rectifier based on predictive current control. The nonlinear controller is consisted of nonlinear track differentiators (TD) and special nonlinear function of the error. It improves dc voltage response velocity, restrains overshoot and enhances robustness against load change. In addition, the sinusoidal ac current and unity power factor is also achieved. The simulation results are provided to verify the validity of the proposed control strategy.

A novel control strategy for current-source rectifiers with space vector modulation

Current-source rectifiers have been becoming more and more popular in the fields of SMES, UPS and reactive power compensation, etc. But the power factor cannot be adjusted to an arbitrary value accurately and transient oscillations will appear for the presence of LC filter with only a dc current loop. In this paper, a novel double closed-loop control strategy based on the model of CSR in the synchronously rotating reference frame which has inherent input filter damping function is proposed. The proposed method introduces another dq current loop to overcome the drawbacks above. In this paper, the CSR model in the synchronously rotating coordinates is introduced and the proposed control strategy details are described first of all. Then a SVM switching pattern is presented, which is easy to be implemented on DSP and presents low total harmonic distortion factor. The stability of the control system is also analyzed. At last, the CSR model is established in MATLAB/SIMULINK. The simulation results show that the active and reactive currents can follow the reference currents accurately and the oscillations can be suppressed.