Trillion Q. Zheng

Field Oriented Control of Linear Induction Motor Considering Attraction Force & End-Effects

This paper presents a field oriented control scheme of the linear induction motor (LIM) in order to achieve high performance of the machine. The dynamic model of LIM taking into account end-effects is derived. Then the modified mechanical load equation considering the effect of the attraction force on the performance of linear induction motor is analyzed. Finally the control strategy based on field oriented control is presented. The simulation results are presented to show the control system has the quick speed response and the robust thrust characteristics

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

Suppressing EMI in Power Converters via Chaotic SPWM Control Based on Spectrum Analysis Approach

This paper aims at developing a spectrum analysis approach for suppressing the electromagnetic interference (EMI) in power converters via chaotic sinusoidal pulse width modulation (CSPWM) control signals based on double Fourier series. In detail, we prove that the total harmonics of power converters under CSPWM control are the same with those of power converters under traditional SPWM control. Then, we introduce a novel spectrum analysis approach based on sawtooth carrier and double Fourier series. Moreover, a photovoltaic (PV) inverter is used to validate the proposed spectrum analysis approach based on the calculation of the output voltage spectrum for CSPWM control signals. In particular, this proposed method can also be used for the spectrum analysis of multiperiodic signals. Indeed, this developed spectrum analysis approach provides a rigorous theoretical foundation for the CSPWM control in EMI suppression.

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

Research on modular multilevel converter based STATCOM

A new modular multilevel converter (MMC) based static synchronous compensator (STATCOM) is proposed and hereafter called M-STATCOM. The new shunt compensator, features with the characteristics such as high modularity, availability, low generation of harmonics, etc., is well suitable for medium- or high-voltage utility grid without line-frequency transformers. M-STATCOM can not only be controlled in static var generating condition for reactive power compensation purpose, but also be suitable for the comprehensive mitigation of all the power quality problems under the three-phase unbalanced power systems. The structural characteristics and operating principles of M-STATCOM for both static var generating condition and comprehensive compensating condition are analyzed in detail. Moreover, two corresponding control schemes were proposed. The effectiveness of the proposed control strategy and feasibility of analysis is validated by the simulation results.

Improved Deadbeat Current Controller with a Repetitive-Control-Based Observer for PWM Rectifiers

The stability of PWM rectifiers with a deadbeat current controller is seriously influenced by computation time delays and lowpass filters inserted into the current-sampling circuit. Predictive current control is often adopted to solve this problem. However, grid current predictive precision is affected by many factors such as grid voltage estimated errors, plant model mismatches, dead time and so on. In addition, the predictive current error aggravates the grid current distortion. To improve the grid current predictive precision, an improved deadbeat current controller with a repetitive-control-based observer to predict the grid current is proposed in this paper. The design principle of the proposed observer is given and its stability is discussed. The predictive performance of the observer is also analyzed in the frequency domain. It is shown that the grid predictive error can be decreased with the proposed method in the related bode diagrams. Experimental results show that the proposed method can minimize the current predictive error, improve the current loop robustness and reduce the grid current THD of PWM rectifiers.

Synchronous PI control for three-phase grid-connected photovoltaic inverter

This paper presents mathematical modeling procedure of three-phase grid-connected photovoltaic inverter. Presents synchronous PI current control strategy and the method for adjuster design. The typical waveforms of grid voltage, grid current and harmonics of grid current are carried out on a 100kW photovoltaic inverter, which can provide some guidelines for engineers to analyze, design and implement.

Harmonic analysis of traction networks based on the CRH380 series EMUs accident

The harmonic component introduced by the high-speed electric multiple units(EMUs) can cause resonance phenomenon in traction networks. A similar resonance accident occurred when the novel CRH380 Series EMUs were running in the Beijing-Shanghai high-speed railway. According to the operation parameters, this paper built the chain network model of the traction power supply system and analysed the influence of harmonic current using the matrix calculation function of MATLAB. The model was based on the uniform transmission lines analysis and combined the characteristics of the multi-conductor transmission. The reason of the accident was analyzed and a reliable strategy to solve the resonance problems was proposed.

Application of feedback linearization strategy in voltage fault ride-through for photovoltaic inverters

Fault ride-through specifications listed in modern transmission and distribution grid codes specify that photovoltaic system have to operate under grid faults. In the classic strategies used in photovoltaic systems the power delivered to the grid remains constant when a fault occurs. As a consequence, the system should operate with increasing inverter current, which may result in damage. Noticing the PV arrays special characteristics,this paper presents new strategy for photovoltaic systems which ensures the current levels remaining within the designed limits. In addition,a nonlinear feedback controller based on feedback linearization is used to control the inverter. Simulation results are presented in order to validate the proposal. The results include performance of different voltage dips. The proposed control strategy permits the inverter operates in any fault situation without over currents as well as delivering sinusoidal currents. In addition, The dynamic performance of LVRT is improved by using the proposed controller.

Stability Improvement of V/Hz Controlled PWM Inverter-fed Induction Motors Drives

Three-phase induction motor drive systems driven by V/Hz controlled PWM voltage source inverter, which have been widely used in the industrial applications, have often suffered undesirable sustained oscillations in the light loaded state and in the low frequency range. In this paper, we propose a new method which is effective and simple to improve the stability of V/Hz controlled induction motor drives. This method is robust, regardless of the parameters of the motors, the inverters and the operating conditions, and is suitable for general-purpose induction motor drive systems. Simulation and experimental results are presented to verify the validity of this proposed stabilizing control method