A new deadbeat type of direct torque control is proposed, analyzed and experimentally verified in this paper. The control is based on stator and rotor flux as state variables. This choice of state variables allows a graphical representation which is transparent and insightful. The graphical solution shows the effects of realistic considerations such as voltage and current limits. A position and speed sensorless implementation of the control, based on the self-sensing signal injection technique, is also demonstrated experimentally for low speed operation. The paper first develops the new, deadbeat DTC methodology and graphical representation of the new algorithm. It then evaluates feasibility via simulation and experimentally demonstrates performance of the new method with a laboratory prototype including the sensorless methods.

Stator and Rotor Flux Based Deadbeat Direct Torque Control of Induction Machines. Revision 1

To achieve instantaneous control of induction motor torque using field-orientation techniques, it is necessary that the phase currents be controlled to maintain precise instantaneous relationships. Failure to do so results in a noticeable degradation in torque response. Most of the currently used approaches to achieve this control employ classical control strategies which are only correct for steady-state conditions. A modern control theory approach which circumvents these limitations is developed. The approach uses a state-variable feedback control model of the field-oriented induction machine. This state-variable controller is shown to be intrinsically more robust than PI regulators. Experimental verification of the performance of this state-variable control strategy in achieving current-loop performance and torque control at high operating speeds is included.

https://ieeexplore.ieee.org/iel5/28/4504948/04504956.pdf

Performanceof FeedforwardCurrentRegulators forField-Oriented Induction Machine Controllers

This paper investigates the use of multilevel conversion in dc–dc applications that require a large voltage conversion ratio. A quantitative method that can serve as a guide to compare and design multilevel topologies for large conversion ratio applications is presented. The proposed method keeps the conduction loss and switching loss constant across the different converters and employs the passive component volume as the single performance metric. As examples, flying capacitor multilevel converters and hybrid switched-capacitor (SC) converters are compared to conventional two-level buck converters, and are shown analytically to have significantly reduced passive component size. Three converter prototypes are implemented, based on the presented methodology to experimentally validate the method as well as demonstrate the advantages of multilevel and hybrid SC converters.

An Analytical Method to Evaluate and Design Hybrid Switched-Capacitor and Multilevel Converters

Linear induction machines dynamics may not be as fast as that of their rotary counterparts due to a larger air gap, a bigger leakage flux, and end effect. Direct thrust control can speed up their dynamics substantially with rather high pulsations, while vector control facilitates a smoother performance but slower dynamics. In this paper, an analogy between the two control methods, when they are applied to the linear machines, is proved first. The analogy is then used to justify combining the selected parts of the two control methods to come up with a control method that provides faster dynamics than vector control and smother performance than direct thrust control. The proposed control method is realized by getting rid of demanding parts of the two conventional control methods. End effect is also considered in the modeling and control system design. Extensive simulation results confirmed by experimental results prove improved motor performances under the proposed control method. The proposed control is particularly suitable for linear applications that need fast dynamics and smooth operation.

Combined Vector and Direct Thrust Control of Linear Induction Motors With End Effect Compensation

In recent years, long-distance transportation systems have been increasingly used in the factory. The high cost of the linear synchronous motor (LSM) at the initial stage, however, is a problem. This paper proposes that a discontinuous stator permanent-magnet LSM can decrease this initial cost. The motor composed of a stator block (accelerator, reaccelerator, and decelerator) and a free-running section has problems with restarting, however, when the mover stops in the free-running section. As for discontinuous arrangement of the stator block proposed newly, to resolve this problem, one or two stators always overlap the mover. This arrangement can always supply a thrust force to the mover. However, the problem with this system is that, because one inverter is connected to each stator, the number of inverters increases. Moreover, the structure of the control system becomes complicated. Therefore, the number of inverters is decreased by changing the output point of the inverter using a solid-state relay linked to the stator block (the section). This paper describes the section change method of the stator block. This drive method is verified by carrying out experiments and simulation of various drive patterns.

Driving Method of Permanent-Magnet Linear Synchronous Motor With the Stationary Discontinuous Armature for Long-Distance Transportation System

The traction characteristics of a linear induction motor (LIM) are quite different from those of a rotary induction motor (RIM) due to the parameters variations caused by longitudinal end effect, transversal edge effect, and so on. The conventional indirect field-oriented control (IFOC) scheme of the LIM based on flux attenuation compensation is not suitable for high-power traction drives due to the deviation of current and thrust characteristics. In this paper, the traction characteristics of the LIM and RIM are compared from different perspectives. The performance of different control schemes of the LIM is discussed with consideration of the output limitations of the inverter. The IFOC scheme based on optimized slip frequency for the LIM is proposed. By dynamically adjusting the d- and q -axis reference currents and corresponding closed-loop control, the output thrust of the LIM is shifted close to the peak operation point. The average output thrust of the LIM can be increased without increasing the primary current, which can reduce the influence of end and edge effects on thrust performance. The effectiveness of the proposed scheme is verified by both simulation and experiments on an LIM metro vehicle.

An Improved Indirect Field-Oriented Control Scheme for Linear Induction Motor Traction Drives

This paper presents the development of the single side ironless Halbach permanent magnet linear synchronous motor (PMLSM) for a novel electromagnetic suspension (EMS) maglev vehicle. The basic structure of the propulsion motor and the vehicle are firstly described. Then the thrust and normal force of the ironless PMLSM are analyzed. The configuration of the propulsion system and field oriented control (FOC) scheme of the motor are introduced. Single bogie prototype maglev vehicle have been developed and dynamic experiments have been performed on the 204m test line. The experimental results prove the feasibility of the motor for propulsion of the novel maglev vehicle.

Development of ironless Halbach permanent magnet linear synchronous motor for traction of a novel maglev vehicle

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q -axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method.

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

Due to the existence of end-effects and the changing operational conditions, the parameters of linear induction motor (LIM) are variable. In this paper, model reference adaptive method is applied to the parameter identification of linear induction motor. Based on the proposed method, the magnetizing inductance and secondary resistance, which are both the most variable in the equivalent circuit of LIM due to end-effects, can be identified on-line simultaneously. Simulation and experiment results show great performance of the proposed scheme. It can be used in the high performance control of LIM.

On-line parameter identification of linear induction motor based on adaptive observer

The three-level neutral-point-clamped inverter used in the variable frequency system has the characteristics of a wide frequency range, and the pulsewidth modulation (PWM) strategy needs to be designed for the low-frequency region with low modulation index and the high-frequency region with low carrier ratio, respectively. The traditional carrier-based PWM (CBPWM) is simple to implement, but in the low-frequency region, CBPWM will cause narrow pulse and output voltage distortion; while in the high-frequency region, CBPWM can only achieve the synchronized modulation with half-wave symmetrical (HWS) and three-phase symmetrical (TPS) waveforms when the carrier ratio is an odd integer multiple of three, and it cannot realize the square-wave modulation. To solve the defects of CBPWM, this article proposes improved CBPWM (ICBPWM) I, which can avoid narrow pulse and generate line voltage accurately at any low modulation index, ICBPWM II, which can ensure the voltage to meet TPS and HWS when the carrier ratio is an arbitrary integer multiple of three, and ICBPWM III, which can achieve square-wave modulation, separately. On this basis, by using ICBPWM I, ICBPWM II, and ICBPWM III in combination, a hybrid ICBPWM strategy with wide frequency range is further proposed. Finally, the proposed strategy is verified by simulation and experiment.

Ke Wang

Papers

An Improved Indirect Field-Oriented Control Scheme for Linear Induction Motor Traction Drives

Development of ironless Halbach permanent magnet linear synchronous motor for traction of a novel maglev vehicle

An Improved Torque and Current Pulsation Suppression Method for Railway Traction Drives Under Fluctuating DC-Link Voltage

On-line parameter identification of linear induction motor based on adaptive observer

Hybrid Improved Carrier-Based PWM Strategy for Three-Level Neutral-Point-Clamped Inverter With Wide Frequency Range