Incorporating control trajectories with the direct torque control scheme of interior permanent magnet synchronous motor drive

Interior permanent magnet (IPM) synchronous machines have gained increased attention for applications in electric vehicle, variable speed wind turbine, industrial drives, etc., because of their high torque density, wider speed range and compact construction. The authors present a detailed analysis and modelling of control trajectories and incorporate those trajectories in the direct torque control (DTC) scheme of an IPM synchronous motor drive, for constant-torque and constant-power operating regions. The control trajectories are implemented on a real-time digital signal processor. Because the inputs to the inner torque control loop of DTC are the references for the torque and the amplitude of the stator flux linkage (λ_s), they are transformed in the T-λ_s plane, than in the i_d - i_q plane in the indirect control. The modelling and experimental results are presented. Results show very good dynamic and steady-state performances of direct torque controller, incorporating these control trajectories.     

SR电机调速系统控制器设计

利用DSP的速度及硬件资源优势,设计了相应的外围检测、电流限幅、倍频、PWM调理等功能电路以及保护电路,使控制系统结构紧凑,可靠性高.实现了系统的电压PWM斩波控制方式下的稳定运行.     

Direct torque and flux control of an IPM synchronous motor drive using a backstepping approach

A novel direct torque and flux controlled interior permanent magnet synchronous motor (IPMSM) drive using an adaptive backstepping technique is presented. Closed-loop regulation of the speed, torque and stator flux linkage is achieved by a non-linear controller. Using Lyapunov analysis, the stability of the controller is guaranteed. The reference voltage vectors are generated by a space vector modulation (SVM) unit, which replaces the switching table in the conventional direct torque control (DTC) scheme. While retaining its main advantages, the proposed backstepping controller features reduced torque and flux ripples as compared to the classical DTC. On the one hand, a comparison with the proportional-integral (PI) direct torque and flux control (DTFC) scheme shows that the proposed approach is superior. Experimental results confirm the effectiveness of the proposed method.     

Speed controller design of direct torque control system for induction motors by using adaptive supervisory Fuzzy-CMAC

A model-free approach was used to develop an adaptive supervisory Fuzzy-cerebellar model articulation controller (ASFCMAC) for a direct torque control system for an induction motor without shaft encoder. The two parts of the ASFCMAC are a supervisory controller for limiting tracking error to a bounded range and a Fuzzy-cerebellar model articulation controller subsystem for learning and approximating system dynamics. The ASFCMAC parameters are tuned according to adaptive rules derived from Lyapunov stability theory. Simulations and experimental comparisons with adaptive Fuzzy-cerebellar model articulation controller, adaptive cerebellar model articulation controller, fuzzy logic control, and proportional–integral control show that the proposed ASFCMAC has a superior root mean square error in operation over a wide range of speeds.     

On-line instantaneous torque control of a switched reluctance motor based on co-energy control

An on-line instantaneous torque control technique for a switched reluctance motor operating in the saturation region is presented. The proposed methodology is realised via the control of the instantaneous output torque of each excited phase by regulating its associated co-energy to follow a co-energy profile. As the parameters of the feedback controller are independent of the motor parameters in the analysis of the co-energy control system with the proposed methodology, the design of the proposed controller is simple when compared to that for traditional current controllers. Smooth shaft torque is obtained by torque sharing among the active phases during commutation. Simulation and experimental results confirm that the highfrequency torque ripple is reduced using the proposed algorithm.     

Dynamic performance of a vector-controlled five-phase synchronous reluctance motor drive: an experimental investigation

Multi-phase ac motor drives are nowadays considered for various applications due to numerous advantages that they offer when compared with their three-phase counterparts. In principle, control methods for multi-phase machines are the same as for three-phase machines. The operation of an indirect vectorcontrolled five-phase synchronous reluctance machine with current control in the stationary reference frame is analysed. Performance, obtainable with ramp-comparison current control, is illustrated for a number of operating conditions on the basis of experimental results. Full decoupling of rotor flux control and torque control is realised. Excellent dynamic response is achieved during acceleration, deceleration and reversing transients of machine.     

Modified Elman neural network controller with improved particle swarm optimisation for linear synchronous motor drive

A modified Elman neural network controller is proposed to control the mover of a permanent magnet linear synchronous motor (PMLSM) servo drive to track periodic reference trajectories. First, the dynamic model of the PMLSM drive system is derived. Next, a modified Elman neural network is proposed to control the PMLSM. Moreover, the connective weights of the modified Elman neural network are trained online by back-propagation (BP) methodology. However, the learning rates of the online-training weights are usually selected by trial-and- error method, which is time-consuming. Therefore an improved particle swarm optimisation (IPSO) is adopted in this study to adapt the learning rates in the BP process of the modified Elman neural network to improve the learning capability. Finally, the control performance of the proposed modified Elman neural network controller with IPSO is verified by the simulated and experimental results.     

Design and implementation of an H1 controller for a micropermanent-magnet synchronous motor position control system

Design and implementation of an H_infin controller for a micropermanent- magnet synchronous motor position control system is proposed. The diameter of the micromotor is only 6 mm. In addition, the weighting functions of the H_infin controller are selected using the genetic algorithms. A state-space H_infin controller, obtained using a systematic design procedure, is incorporated in a closed-loop position control micromotor system. The system has good performance, including fast transient responses and good load disturbance rejection responses, although its encoder is only 100 pulses/revolution. A digital signal processor, TMS320F2407, is used to execute the position control algorithms. Experimental results validate the theoretical analysis and show the correctness and feasibility of the proposed method. An advanced controller design is proposed for a micromotor.     

Design and implementation of an adaptive inverse controller for a micro-permanent magnet synchronous motor control system

An adaptive inverse controller design for a micro-permanent magnet synchronous motor control system is proposed. The adaptive inverse controller is constructed by using an adaptive model and an adaptive controller. The parameters of the adaptive model and adaptive controller are on-line tuned. By using the proposed adaptive inverse controller, the transient responses, load disturbance responses and tracking responses of the control system are improved. To detect the shaft rotor position, a micro-encoder is attached with the micro-permanent magnet synchronous motor. The micro-encoder provides only 100 pulses/revolution because of its space limitation. As a result, the resolution of the position signal and speed signal is not good enough. In order to improve the resolution, a state estimator is proposed here. By using the proposed state estimator, the control system can be operated from 1 to 25 000 r/min. The adaptive inverse control algorithm and the state estimation algorithm are executed by a digital signal processor, TMS320F28335. In addition, the proposed adaptive inverse control algorithm can be applied to the position control for the micro-permanent magnet synchronous motor as well. Several experimental results validate the theoretical analysis. The experimental results show that the proposed system has good performance including transient responses, load disturbance responses, and tracking responses.     

Improved direct torque control of induction motor with dither injection

In this paper, a three-level inverter-fed induction motor drive operating under Direct Torque Control (DTC) is presented. A triangular wave is used as dither signal of minute amplitude (for torque hysteresis band and flux hysteresis band respectively) in the error block. This method minimizes flux and torque ripple in a three-level inverter fed induction motor drive while the dynamic performance is not affected. The optimal value of dither frequency and magnitude is found out under free running condition. The proposed technique reduces torque ripple by 60% (peak to peak) compared to the case without dither injection, results in low acoustic noise and increases the switching frequency of the inverter. A laboratory prototype of the drive system has been developed and the simulation and experimental results are reported.     

Performance investigation of modified hysteresis current controller with the permanent magnet synchronous motor drive

This study presents complete permanent magnet synchronous motor (PMSM) drive scheme along with mathematical model of motor and inverter. Speed proportional integral (PI) controller parameters are designed in discrete time domain. Stability of the speed controller is observed with respect to motor-load parameters. A modified hysteresis current control scheme is implemented for the drive and a detailed comparative study is done with conventional hysteresis current control scheme. Merits of the modified hysteresis current controller over conventional hysteresis current controller are investigated with both simulation and experimental results.     

Sensorless interior permanent magnet synchronous motor drive system with a wide adjustable speed range

The authors propose a novel extended flux estimating method for an interior permanent magnet synchronous motor. By using the proposed method, an extended flux can be systematically derived. Then, the shaft position and speed of the motor can be obtained. Starting from a standstill and at a low-speed range control, a current-slope estimating method is used to replace the extended flux method because the estimating extended flux decreases as the motor speed is reduced. By combining the extended flux and the current-slope estimating methods, the interior permanent magnet synchronous motor drive system can be controlled in a wide range with satisfactory performance. The adjustable speed range is from 1 to 2000 r/min. In addition, the system performs fast transient responses and good load-disturbance responses. Moreover, a sensorless position control system has been well developed based on the speed control drive system. A TMS 320LF2407 digital signal processor is used to execute the rotor position estimation, rotor speed estimation, current-loop control, speed-loop control and position-loop control algorithms. The hardware circuit therefore is very simple. Several experimental results are provided to validate the theoretical analysis.     

Optimisation techniques for a hysteresis current controller to minimise torque ripple in switched reluctance motors

The switched reluctance (SR) motor has many benefits owing to its low cost, simple design, rugged construction and comparatively high torque-to-mass ratio. Unlike DC and induction motors, the SR motor is intended to operate in deep magnetic saturation to increase the output power density. Because of the saturation effect and the variation of magnetic reluctance with respect to rotor position, all the relevant characteristics of the machine are highly non-linear functions of both rotor position and phase current. The ultimate outcome of all these non-linearities is that the generated torque contains significant ripples. The non-linearities in the SR motor have been extensively studied and many control strategies to reduce the generated torque ripples have been proposed in the literature. Modulation of phase current profile for generating torque in the SR motor with minimum ripples was the focus of most of the research. However, the main challenge to minimise the torque ripple is to design a current controller that is able to track the modulated phase current. In this work, new techniques to optimise the widely used hysteresis current controller are studied, and experimental verifications under closed-loop speed control with the modulated reference current data are presented. The experimental results indicate that the torque ripple is reduced to lie within 5% of the desired steady torque using the proposed optimisation techniques.     

Evolution of local to global minimum torque ripples of direct torque control for induction motor drives

This study discusses the evolution of the local minimum to global minimum torque ripples of the direct torque control of induction motor drives. This study will show that the previous minimum torque ripple design is not the global minimum but a local minimum root-mean-square (RMS) torque ripple. To show this, the study finds the optimal initial torque error, which makes the global minimum torque ripple, and then the related global minimum RMS torque ripple. Moreover, after finding the optimal initial torque error and its related global minimum RMS torque ripple, this study derives the evolution of the initial torque ripple error, under the local minimum RMS torque ripple control strategy. Furthermore, this study also proves that under the local minimum RMS torque ripple control strategy, the local minimum torque ripple will converge to the global minimum value.     

Very low speed performance of active flux based sensorless control: interior permanent magnet synchronous motor vector control versus direct torque and flux control

This study is focused on very low speed performance comparison between two sensorless control systems based on the novel 'active flux' concept, that is, the current/voltage vector control versus direct torque and flux control (DTFC) for interior permanent magnet synchronous motor (IPMSM) drives with space vector modulation (SVM), without signal injection. The active flux, defined as the flux that multiplies iq current in the dq-model torque expression of all ac machines, is easily obtained from the stator-flux vector and has the rotor position orientation. Therefore notable simplification in the rotor position and speed estimation is obtained. For IPMSM, a stator-flux observer is employed based on combined current and voltage models, with speed-dependent smooth transition between them using a PI compensator of flux error. Comparative experimental results using both sensorless control systems are presented to verify the principles and to demonstrate the effectiveness of the active flux observer at very low speeds from 20 to 2 rpm (1-0.1 Hz).     

Modelling and predicting of a switched reluctance motor drive using radial basis function network-based adaptive fuzzy system

A novel fuzzy-neural system, which is referred to as a radial basis function network-based adaptive fuzzy system (RBFN-AFS), is presented, to model the switched reluctance machine (SRM) and predict the dynamic performances in an SRM drive system. First, we use an indirect method to measure the phase flux linkage of a 6/4 SRM and then use the co-energy method to calculate phase torque characteristics. Secondly, the RBFNAFS is designed to learn and train the SRM in the knowledge of the electromagnetic characteristics by using the hierarchically self-organising learning algorithm. This modelling scheme does not require any prior information about the SRM system apart from the input and output signals, and has good capability of generalisation and excellent convergent speed. Then, an RBFN-AFS current-dependent inverse flux linkage model and an RBFN-AFS torque model are used to simulate the various transient and steady-state performances of the 6/4 0.55 kW SRM. The simulation and experimental results based on a DSP drive platform are reported to show that the modelling scheme has good estimation performance under different operation conditions of the SRM.     

Sensorless permanent-magnet synchronous motor drive using a reduced-order rotor flux observer

A sensorless permanent-magnet synchronous motor (PMSM) drive is developed. A second-order Luenberger observer is used to estimate the position of the rotor flux and hence the rotor speed. The observer is computationally efficient as it has a simple structure and does not involve mechanical parameters. An integral-feedback method is adopted for the estimation of the rotor speed. The inner current loop is realised using a decoupling and diagonal internal model control algorithm. Details of the sensorless control system are given and the feasibility of the proposed method is verified through simulation and experiments. Satisfactory estimation accuracy is obtained even when the drive operates at very low speeds and also during rotor speed reversals.     

Introducing dynamic behavior of magnetic materials into a model of a switched reluctance motor drive

Dynamic hysteretic effects of magnetic materials are usually neglected in actuators modeling. In order to take into account these effects, we coupled a two-dimensional finite-element (FE) model in an original way with a magnetic equivalent circuit by using dynamic hysteretic flux tubes (DHFT). As an example of an application, we present the model of an ultrafast switched reluctance motor, in which the control of the power converter is of major importance, and where iron losses can reach critical values.