Performance evaluation of a direct torque controlled drive in thecontinuous PWM-square wave transition region

This paper investigates the operation of a direct torque controlled drive when operating under transient conditions and when operating in overmodulation conditions or in the “transition region” to six-step operation. The direct torque control is a dead-beat control of the torque and flux magnitude. In the steady-state, the stator voltage vector which drives the torque and flux to the reference value is calculated during each fixed switching period. Under transient or overmodulation conditions, an alternative switching algorithm must be used since dead-beat control is no longer possible. Two alternatives are presented for operation in overmodulation. The first involves a determination of the switching state a priori, and calculating the duty cycle for each phase based on the torque and flux error. A much simpler scheme is presented which utilizes the voltage reference vector from the direct torque control algorithm. This scheme, although not resulting in dead-beat control, is shown to provide very satisfactory performance in overmodulation. The direct torque control method shows great promise for light traction applications where a large quasi-constant power region is required. The scheme operates very satisfactorily in overmodulation, compared with existing current regulated PWM-based schemes, due to the fact that the voltage space vectors are directly controlled. A complete experimental evaluation of the proposed scheme operating in the transition region is also given     

Stator flux based space-vector modulation and closed loop control of the stator flux vector in overmodulation into six-step mode

This paper presents closed loop control of stator flux vector in a wide operating range that can be used in torque control. A predictive control achieves zero phase error at constant switching frequency. Space vector modulation based on stator flux error vector is used to achieve control of stator flux over the entire range including overmodulation and six-step. During dynamics the fastest possible flux vector change is employed similar to the direct torque control. Experimental results are provided for a wide speed range and effect of parameter variation is studied.     

DTFC-SVM motion-sensorless control of a PM-assisted reluctance synchronous machine as starter-alternator for hybrid electric vehicles

Permanent magnet-assisted reluctance synchronous machine (PM-RSM) starter alternator systems are credited with good performance for wide speed range in hybrid electric vehicles. This paper proposes a motion-sensorless motor/generator control of PM-RSM from zero speed up to maximum speed, using direct torque and flux control with space vector modulation. A quasioptimal stator flux reference with a flux versus torque functional is proposed. A stator flux observer in wide speed range uses combined voltage-current models for low speeds, and only the voltage model for medium to high speeds, both in proportional-integral closed loop. A novel rotor speed and position observer with a fusion strategy employs signal injection and only one D-module vector filter in stator reference for low speed, combined with a speed observer from the stator flux vector estimation-for medium-high speed. The proposed system is introduced piece by piece and then implemented on a dSpace 1103 control board with a 350-A metal-oxide-semiconductor field-effect transistor-pulse-width modulation converter connected to a 42-Vdc, 55-Ah battery, and a 140-Nm peak torque PM-RSM. Extensive experimental results from very low speed to high speed, regarding observers and drive responses, including artificial loading (motoring and generating), seem very encouraging for future starter-alternator systems.     

Predictive Torque Control of Induction Machines Using Immediate Flux Control

This paper proposes a new concept for the control of voltage-source inverter (VSI)-fed induction machines. The method uses a predictive algorithm and can be split into two parts. The purpose of the first part, i.e., predictive torque control (PTC), is to predict the stator reference flux vector corresponding to the reference torque at the end of the sampling interval. The second part of the method provides accurate tracing of the stator reference flux by selecting either an active or a zero voltage vector. This approach is called immediate flux control (IFC), where two possible variants are suggested. In the first variant, a simple and fast algorithm obtains minimal stator flux error by impressing either an active or a zero voltage vector throughout the entire sampling interval. Consequently, the switching frequency becomes very low, but current and torque ripple are considerable. The second IFC variant generates the stator flux more accurately by applying an active voltage vector only throughout a calculated time slot within a sampling interval, whereas, during the remaining time of the sampling interval, a zero voltage vector is impressed. As a result, higher switching frequency arises, but it is still lower than that with space vector modulation. Both IFC variants, together with PTC, require minimal processing time and were efficiently implemented in a digital signal processor, which controlled a 3-kW induction machine drive. The obtained experimental results confirm the validity of the proposed approach.     

基于SVPWM的永磁同步电动机直接转矩控制

针对永磁同步电动机直接转矩控制系统转矩和定子磁链脉动问题,采用电压空间矢量脉宽调制(SVPWM)的永磁同步电动机直接转矩控制方法。根据在每一个控制周期内,计算出参考磁链和所估计磁链的偏差,选择相邻非零矢量和零矢量,并精确地计算出各自的作用时间,然后利用线性组合法将其合成为新的电压矢量。仿真结果表明,所提出的控制方案是有效的,明显地改善转矩和磁链脉动,并且有很好的动态和稳态性能。     

An improved flux observer based on PLL frequency estimator for sensorless vector control of induction motors

This paper presents an improved method of flux estimation for sensorless vector control of induction motors based on a phase locked loop (PLL) programmable low-pass filter (LPF) and a vector rotator. A PLL synchronized with the voltage vector is used for stator frequency estimation. The pure integration of the stator voltage equations is difficult to implement and LPFs with a fixed cutoff provide good estimates only in the relatively high frequency range-at low frequencies, the estimates fail in both magnitude and phase. The method proposed corrects the above problem for a wide range of speeds. Simulations and experimental results on a 0.25-hp three-phase induction machine verify the validity of the approach.     

永磁同步电机矢量控制中死区补偿技术的研究

本文针对永磁同步电机矢量控制系统,分析了死区电压矢量对三相输出电压的影响以及死区电压矢量与定子电流方向的关系,提出了一种基于SVPWM矢量控制的死区补偿方法。定子电流矢量角根据计算得出,避免了传统方法在相电流过零处由于电流方向检测不准而影响补偿效果。该方案无需增加硬件电路,对软件进行修改即可实现。仿真试验结果证实了该方法的有效性。     

Voltage modulation factor of the magnetic flux control PWM methodfor inverter

The voltage modulation factor of the magnetic flux control pulse-width modulation (PWM) method is discussed. The modulation factor is derived from a theoretical study on the flux locus produced from the inverter output voltage. The derivation is based on the fact that the fundamental component of the inverter output voltage is proportional to the radius of the flux locus. It is shown theoretically that the voltage modulation factor is expressed by the content of a zero vector in one cycle of the selected PWM pattern of the space vector expression. The modulation factor of the magnetic flux control PWM method is calculated. The modulation factor can be varied from zero to 12/π². The output voltage of the magnetic flux control PWM method can be controlled by the modulation factor linearly from zero up to overmodulation. The simulation and experimental results are also shown     

Speed-sensorless sliding-mode torque control of an induction motor

Novel induction motor control optimizing both torque response and efficiency is proposed in the paper. The main contribution of the paper is a new structure of rotor flux observer aimed at the speed-sensorless operation of an induction machine servo drive at both low and high speed, where rapid speed changes can occur. The control differs from the conventional field-oriented control. Stator and rotor flux in stator fixed coordinates are controlled instead of the stator current components in rotor field coordinates i_sd and i_sq. In principle, the proposed method is based on driving the stator flux toward the reference stator flux vector defined by the input command, which are the reference torque and the reference rotor flux. The magnitude and orientation angle of the rotor flux of the induction motor are determined by the output of the closed-loop rotor flux observer based on sliding-mode control and Lyapunov theory. Simulations and experimental tests are provided to evaluate the consistency and performance of the proposed control technique     

A novel vector control scheme for transistor PWM inverter-fedinduction motor drive

A novel vector control scheme for a transistor pulse-width-modulation (PWM)-inverter-fed induction motor drive is presented. The system is based on a current control loop that consists of two independent nonlinear controllers that regulate the DC (field-oriented) components of the stator current vector. Three-level hysteresis comparators are used as current controllers. The outputs of the comparators select the appropriate inverter output voltage vectors via a switching erasable programmable ROM (EPROM) table. The theoretical principle of this method is discussed. Simulation and experimental results that illustrate the operation of the proposed system and performance in comparison with the other known schemes based on two-level hysteresis comparators are presented     

无传感器交流传动技术的展望

在电机轴上无机械速度传感器的可控交流电机驱动，由于其低廉的价格和较高的可靠性，一直备受关注。为了取代传感器，它通过测量定子电流和电机端电压得到转子速度信息。矢量控制传动需要估计定子或转子磁通基波的大小和空间位置。为此需要使用开环估计器或闭环观测器，它们在准确性、鲁棒性以及对模型参数变化的敏感性等性能上均不相同。通过信号注入即利用电机的各向异性，可以获得零速范围附近的动态性能和稳态速度精度。本文使用复杂空间矢量的信号流程图来形象地描述交流电机无传感器的控制系统。     

Steady-state and transient performance evaluation of a DTC schemein the low speed range

In this paper, a direct flux and torque control scheme for industrial application is analyzed in order to emphasis the drive performance at standstill and in the low speed range. The control strategy utilizes the torque and rotor flux commands to determine the reference value of the stator flux. In order to improve the low speed performance a closed loop estimator is employed to evaluate the rotor flux. The validity of the control scheme is verified by simulations and experimental tests of an induction motor drive system     

Extended Voltage Swell Ride-Through Capability for PWM Voltage-Source Rectifiers

Voltage swells are one of the most harmful disturbances present in industrial power systems, being capable of severely damaging, breaking, or tripping converters. In the case of pulsewidth-modulation voltage-source rectifiers (PWM-VSRs), swells first saturate their control system and then force them into six-pulse operation if no precautions are taken. This paper presents an extended ride-through strategy enabling these converters to deal and cope with swells of up to 1.8 p.u. (IEEE Std. 1159 swell definition). The proposed strategy first fully exploits the dc-link voltage capacity by dynamically entering the overmodulation region, and secondly by drawing inductive current in case the former action does not suffice. Dynamic overmodulation makes possible the straight ride-through of 15% and 42% three-phase and single-phase swells, whereas the modulation index supervisor/control loop drawing inductive current enables the ride-through for greater magnitude disturbances, all the while avoiding saturation of the converter control system. This is realized using decision-making space vector modulation, and a control system built over a nonlinear control law directly obtained from the converter complex state variable model. In this way, linear and decoupled$d$–$q$axes dynamics are attained, ensuring a constant dynamic response throughout the whole operating range. Finally, experimental results from a TMS320C32 digital-signal-processor-based 5-kVA laboratory prototype subjected to typical industry single- and three-phase swells ranging from 5% to 50% are presented. These confirm the predicted performance and feasibility of the proposed voltage swell ride-through strategy for PWM-VSRs.     

Full Utilization of the Inverter in Split-Phase Drives by Means of a Dual Three-Phase Space Vector Classification Algorithm

A simple and effective space vector pulsewidth-modulation technique for six-phase voltage-source-inverter-fed split-phase induction motors is presented in this paper. The approach employs dual three-phase space vector modulators equipped with overmodulation schemes that compensate for the voltage gain reduction due to the use of two independently controlled three-phase inverters. It secures full control of the voltage gain up to the maximum achievable gain with negligible low-order harmonics and utilizes a simple classification algorithm for the implementation of the space vector modulation (SVM) in both linear and overmodulation modes. Experimental results are provided to verify the validity of the proposed SVM split-phase approach.     

基于模型参考自适应系统的感应电机控制

采用模型参考自适应法设计了无速度传感器矢量观测器。现以电压模型为参考模型,电流模型为可调模型,推算出速度信息,计算输出控制信号,实现了对感应电机的精确控制;通过Matlab／Simulink对其进行仿真、验证,结果表明,该系统对定子磁链观测精度高,速度估计准确,改善了电机的控制特性。     

Hybrid Cascaded H-Bridge Multilevel-Inverter Induction-Motor-Drive Direct Torque Control for Automotive Applications

This paper presents a hybrid cascaded H-bridge multilevel motor drive direct torque control (DTC) scheme for electric vehicles (EVs) or hybrid EVs. The control method is based on DTC operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a dc source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, even without filtering, using fewer switching devices. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with fewer switching losses, since only the small power cells of the inverter operate at a high switching rate. Therefore, a high performance and also efficient torque and flux controllers are obtained, enabling a DTC solution for multilevel-inverter-powered motor drives.      

Sensorless DTC-SVM for Induction Motor Driven by a Matrix Converter Using a Parameter Estimation Strategy

This paper presents a new direct torque controlled space vector modulated method to improve the sensorless performance of matrix converter drives using a parameter estimation scheme. The flux and torque error are geometrically combined in a new flux leakage vector to make a stator command voltage vector in a deadbeat manner. A new sensorless method of estimating the rotor speed, flux, stator resistance, and rotor resistance is derived and verified with experimental results. Common terms in the error dynamics are utilized to find a simpler error model involving some auxiliary variables. Using this error model, the state estimation problem is converted into a parameter estimation problem assuming the rotor speed is constant. The proposed adaptive schemes are determined so that the whole system is stable in the sense of Lyapunov. The effectiveness of the proposed algorithm is verified by experiments.     

Torque ripple analysis and dynamic performance of a space vector modulation based control method for AC-drives

A constant switching frequency torque control method is presented in this paper, that uses flux error vector based space vector modulation (SVM) to achieve steady state and dynamic control of torque. The effect of SVM switching on torque ripple has been analyzed using "flux ripple vectors". This approach is used to develop an insight of torque ripple and to estimate it for any operating angular velocity. We propose a method of compensation to maintain steady state control of torque in the overmodulation region of operation. During torque dynamic, the optimum maximum switching state vector is selected. This gives a response similar to that obtained using direct torque control (DTC) and direct self control (DSC) methods. The proposed method is verified experimentally.     

Linear control of inverter output voltage in overmodulation

A novel overmodulation strategy for space-vector pulsewidth modulated (PWM) inverters is proposed. The method, which increases the range of linear control of the output voltage by 10%, is based on Fourier series representation of the reference voltage     

基于MRAS的永磁同步电机直接转矩控制系统的研究

研究了一种基于模型参考自适应无速度传感器的永磁同步电机直接转矩控制系统:将永磁同步电机的磁链模型作为参考模型,估算的定子磁链模型作为可调模型,设计了自适应定律对电机的转速与定子电阻同时进行跟踪辨识,使用空间电压矢量调制技术组成了永磁同步电机无速度传感器直接转矩控制系统。仿真实验结果表明该系统获得了近似圆形的定子磁链,在转速与转矩变化时均能准确的估算出电机转速,具有良好的动、静态性能。