A Novel Fuzzy Direct Torque Control System for Three-level Inverter-fed Induction Machine

Diode clamped multi-level inverter （DCMLI） has a wide application prospect in high-voltage and adjustable speed drive systems due to its low stress on switching devices, low harmonic output, and simple structure. However, the problem of complexity of selecting vectors and capacitor voltage unbalance needs to be solved when the algorithm of direct torque control （DTC） is implemented on DCMLI. In this paper, a fuzzy DTC system of an induction machine fed by a three-level neutral-point-clamped （NPC） inverter is proposed. After introducing fuzzy logic, optimal selecting switching state is realized by applying various strategies which can distinguish the grade of the errors of stator flux linkage, torque, the neutral-point potential, and the position of stator flux linkage. Consequently, the neutral-point potential unbalance, the dr/dr of output voltage and the switching loss are restrained effectively, and desirable dynamic and steady-state performances of induction machines can be obtained for the DTC scheme. A design method of the fuzzy controller is introduced in detail, and the relevant simulation and experimental results have verified the feasibility of the proposed control algorithm.

Model Predictive Control-Based Direct Torque Control for Matrix Converter-Fed Induction Motor with Reduced Torque Ripple

To reduce the torque ripple in motors resulting from the use of conventional direct torque control(DTC),a model predictive control(MPC)-based DTC strategy for a direct matrix converter-fed induction motor is proposed in this paper.Two new look-up tables are proposed,these are derived on the basis of the control of the electromagnetic torque and stator flux using all the feasible voltage vectors and their associated switching states.Finite control set model predictive control(FCS-MPC)has then been adopted to select the optimal switching state that minimizes the cost function related to the electromagnetic torque.Finally,the experimental results are shown to verify the reduced torque ripple performance of the proposed MPC-based DTC method.

Model Predictive Direct Torque Control of Permanent Magnet Synchronous Motor (PMSM) with Online Parameter Estimation Based on Extended Kalman Filter

Aiming at the torque and flux ripples in the direct torque control and the time-varying parameters for permanent magnet synchronous motor (PMSM), a model predictive direct torque control with online parameter estimation based on the extended Kalman filter for PMSM is designed. By predicting the errors of torque and flux based on the model and the current states of the system, the optimal voltage vector is selected to minimize the error of torque and flux. The stator resistance and inductance are estimated online via EKF to reduce the effect of model error and the current estimation can reduce the error caused by measurement noise. The stability of the EKF is proved in theory. The simulation experiment results show the method can estimate the motor parameters, reduce the torque, and flux ripples and improve the performance of direct torque control for permanent magnet synchronous motor (PMSM).

A Novel Multilevel Inverter Circuit for the Performance Enhancement of Direct Torque Controlled Induction Motor

Induction motor is the most sought after motor in the industry for excellent performance characteristics and robustness. Developments in the Power Electronic circuitry have revolutionised the induction motor industry leading to the developments in various control strategies and circuits for motor control. Direct Torque Control (DTC) is one of the excellent control strategies preferred by industries for controlling the torque and flux in an induction machine. The main drawback of DTC is the presence of torque ripple which is slightly more than the acceptable limit. There are various parameters that introduce ripples in the electromagnetic torque, one of them being the type of inverter circuit. There are various types of inverter circuits available and the effect of each of them in the production of torque ripple is different. This work is an attempt to identify the influence of various multilevel inverter circuits on the torque ripple level and to propose the best inverter circuit. The influence of multilevel diode clamped inverter and cascaded H bridge inverter circuits on torque ripple minimization, is analysed using simulation studies for identifying the most suitable multilevel inverter circuit which gives minimum torque ripple. The results obtained from the simulation studies are validated by hardware implementation on 0.75 kW induction motor.

Research on Direct Torque Control System Based on Induction Motor

The mathematic model of direct torque control (DTC) was deduced. Two simulating models based on the MATLAB & SIMULINK were established. The emphasis is focused on study of the performance difference of the DTC system with stator flux hexagon and circle trajectories. The simulation waveforms of flux, torque and current characters with two flux trajectories were given. Experiments were carried out in an AC drive system based on induction motor and two-level inverter. A dual-CPU structure was used and the communication with two CPUs was obtained by a dual-port RAM in this system.

An Improved Proportional Integral Estimator of the Stator Resistance for a Direct Torque Controlled Induction Motor

In this paper, an improved PI （proportional integral） stator resistance estimation for a DTC （direct torque controlled） induction motor is proposed. This estimation method is based on an on-line stator resistance correction regarding the variations of the stator current estimation error. In fact, the input variable of the P1 estimator is the stator current estimation error. The main idea is to tune accurately the stator resistance value relatively to the evolution of the stator current estimation error gradient to avoid the drive instability and ensure the tracking of the actual value of the stator resistance. But there is an unavoidable steady state error between the filtered stator current modulus and its estimated value from the dq model of the machine which is due to pseudo random commutations of the inverter switches. This may deteriorate the performance of the proposed fuzzy stator resistance estimator. An offset has been introduced in order to overcome this problem, for different speed command values and load torques. Simulation results show that the proposed estimator was able to successfully track the actual value of the stator resistance lbr different operating conditions.

Sliding mode approach applied to sensorless direct torque control of cage asynchronous motor via multi-level inverter

To improve the robustness and performance of the dynamic response of a cage asynchronous motor,a direct torque control(DTC)based on sliding mode control(SMC)is adopted to replace traditional proportional-integral(PI)and hysteresis comparators.The combination of the proposed strategy with sinusoidal pulse width modulation(SPWM)applied to a three-level neutral point clamped(NPC)inverter brings many advantages such as a reduction in harmonics,and precise and rapid tracking of the references.Simulations are performed for a three-level inverter with SM-DTC,a two-level inverter with SM-DTC and the three-level inverter with PI-DTC-SPWM.The results show that the SM-DTC method achieves better performance in terms of reference tracking,while adoption of the threelevel inverter topology can effectively reduce the ripples.Applying the SM-DTC to the three-level inverter presents the best solution for achieving efficient and robust control.In addition,the use of a sliding mode speed estimator eliminates the mechanical sensor and this increases the reliability of the system.

Direct torque control of doubly fed induction motor using three-level NPC inverter

This article presents the direct torque control (DTC) strategy for the doubly fed induction motor (DFIM) connected to two three-level voltage source inverters (3LVSIs) with neutral point clamped (NPC) structure. This control method allows to reduce the torque and flux ripples as well as to optimize the total harmonic distortion (THD) of motor currents. The use of 3LVSI increases the number of generated voltage, which allows improving the quality of its waveform and thus improves the DTC strategy. The system modeling and control are implemented in Matlab/Simulink environment. The analysis of simulation results shows the better performances of this control, especially in terms of torque and flux behavior, compared to conventional DTC.

磁链分区的磁场增强型永磁电机全速域模型预测直接转矩控制

磁场增强型内置式永磁(flux intensifying interior permanent magnet,FI-IPM)电机的反凸极(L_(q)<L_(d))特性,使得正向d轴电流增强磁场,提高输出转矩的同时,也使得弱磁升速时d轴电流正负交替变化,电流角度变化大,磁链波动大,进而造成转矩脉动大、电流畸变振荡、响应速度慢等问题。针对这些问题,该文提出一种基于磁链分区的磁场增强型内置式永磁电机全速域模型预测直接转矩控制控制策略。根据FI-IPM电机速度运行区域与磁链状态映射关系,构建磁链和转矩预测模型。在此基础上,提出磁链分区控制,引入磁链差值判断增磁和弱磁运行区,并进行磁链补偿,解决不同速度运行域之间切换的震荡和不稳定问题。最后,通过实验验证所提出控制策略的有效性,为该类电机在电驱动系统中的应用提供技术方案。

有源缓冲型逆变器功率解耦技术研究

为实现单级单相升压逆变并能有效抑制直流侧二次纹波电流,提出一种带有源缓冲的电流型逆变器电路拓扑,研究该逆变器的6种电路模态并提出其两模态调制策略和三模态调制策略,设计2种调制策略下的模型预测控制策略,提供主电路参数设计准则。从储能电感电流的最大脉动量与二次纹波含量两方面对2种调制策略进行对比分析,得出了三模态调制策略具有更好纹波抑制效果的结论。对2种调制策略下的逆变器进行仿真分析,仿真结果表明,三模态调制下电路的输出电压总谐波失真率、电感电流相对脉动量与二倍频含量均低于两模态调制下的数据。设计并搭建500VA 48VDC/220V50HzAC有源缓冲型单级单相升压逆变器实验装置,给出了三模态调制下基于模型预测控制的逆变器实验波形,进一步证实了所提研究方案在实现单级升压逆变的同时具有二次纹波抑制能力。

基于MPC的耦合电感飞跨电容双向DC/DC变换器功率均衡解耦控制策略

耦合电感功率变换器因耦合电感阻抗、电感值等参数差异易导致功率不均衡。针对耦合电感飞跨电容双向DC/DC变换器,提出一种基于模型预测控制(MPC)的功率均衡解耦控制策略。通过对变换器原理进行分析,建立基于电感电流解耦的数学模型,得到包括电感电流和飞跨电容电压等6个控制变量的解耦控制方法。在此基础上,提出基于MPC的功率均衡解耦控制策略。同时,为降低MPC算法的运算负荷,根据解耦控制模型重构模型预测价值函数,实现各控制变量独立动态寻优,使系统能在稳定控制输出电压及飞跨电容电压的同时,实现两相耦合电感的功率均衡控制。最后,通过理论分析及实验对所提策略进行有效验证。

智能跑步机异步电机变频调速直接转矩控制

因智能跑步机控制系统存在延时的问题,导致跑步机的运行损耗高、效率低。为此,提出智能跑步机异步电机变频调速直接转矩控制方法。分析异步电机的变频调速效果,构建跑步机控制约束,将模型预测直接转矩控制算法作为非线性内部控制器的控制算法,估计定子磁链后预测定子磁链和电磁转矩,建立合适的目标函数,并采用末端输出控制法获取定子磁链和电磁转矩参考值,对跑步机系统延时加以补偿,完成智能跑步机异步电机变频调速直接转矩控制。实验结果表明,所提方法控制下的智能跑步机振幅曲线波动最小,电磁转矩在(0.5~1.5)N·m之间,稳定后的运行损耗和运行效率控制在67 W和0.77%左右,可有效减小跑步机的电磁转矩脉动,降低运行损耗,提高运行效率,且具有良好的平稳性。

具有中点电压平衡与零序电流抑制的T型三电平逆变器供电六相PMSM-DTC

在三电平六相电机驱动系统中,存在中点电压不平衡及零序电流导致定子电流畸变等问题。为此,该文针对T型三电平逆变器供电的六相永磁同步电机,提出一种具有中点电压平衡与零序电流抑制功能的直接转矩控制(DTC)策略。为实现DTC的快速构建,该策略基于两电平三相电机DTC结构,利用精简后的开关状态,在六相绕组轴线上分别合成满足控制要求的4个电压矢量,然后通过两个滞环比较器结合简单的扇区划分,确定最优电压矢量所在轴线,同时构建中点电压与零序电流控制平面,并对系统在控制平面所处扇区进行判断。在此基础上,根据最优电压矢量所在绕组的相电流iy的极性,实现最优电压矢量的选择,并进一步构建DTC最优开关矢量表。最后,通过实验结果验证了所提控制策略的可行性和有效性。

分数阶双输入Buck变换器的逆向解耦PIλ控制

为提高分数阶双输入Buck变换器的动静态性能,提出一种逆向解耦PIλ控制。首先,基于状态空间平均法建立双输入Buck变换器的分数阶数学模型,推导其分数阶小信号等效模型。随后,分析能量间的耦合关系。基于逆向解耦方法实现变量间的解耦,并推导实现分数阶逆向解耦的必要条件。最后,对解耦系统分别设计分数阶PI控制器,并结合分数阶系统的Nyquist判据证明控制系统的稳定性。仿真结果表明,所提控制策略具有良好的抗干扰性能和动静态调节特性。

无速度传感器的异步电动机模糊自适应PI直接转矩控制

文章针对传统无速度传感器直接转矩控制转速不稳定、超调量大等问题做出两点改进。首先,引入自耦PI对传统MRAS无速度传感器直接转矩控制进行改进,该方法改善无传感器直接转矩控制调速性能、降低超调量、减小稳态误差;其次,针对直接转矩控制具有转矩脉动大、调速性能差等缺点,提出变论域静态模糊自适应PI控制策略,减小转矩脉动并改善调速性能,大大提升了抗负载能力;最后,在Matlab/Simulink仿真环境下进行了仿真并进行分析,证明了上述方法的有效性和可行性。结果表明,相对于传统的无速度传感器直接转矩控制系统,仿真结果显示减小了转速超调量,缩短了转速上升中到达高速工况的响应时间,提升了抗负载能力。

基于六相静止坐标系的永磁容错轮缘推进电机模型预测电流控制

针对六相永磁容错轮缘推进电机在应用传统模型预测电流控制策略时存在计算量大、容错控制策略复杂、电机转矩脉动大的问题,本文提出一种基于六相静止坐标系的模型预测电流控制策略。在固定采样频率下,通过当前时刻转子位置、转速和故障容错控制策略计算出六相定子电流给定值,进而在六相静止坐标系下对六相电流独立地进行2轮预测,通过价值函数寻优确定六相H桥逆变电路的最优开关状态组合,实现对六相永磁容错轮缘推进电机的模型预测电流控制。结果表明:本文提出的基于六相静止坐标系的模型预测电流控制策略具有算法简单、无故障和开路故障下电机转矩脉动小的优点,同时兼顾了传统模型预测电流控制算法动态响应快的特点。

六相全桥逆变器驱动PMSM的简化模型预测电流控制

全桥逆变器电机驱动或称开绕组结构虽然兼具相间电气隔离、容错性能好及器件开关频率低等优点,但存在逆变器输出电压矢量多、冗余严重且控制约束等问题。文中以共直流母线供电的六相全桥逆变器驱动六相永磁同步电机为研究对象,提出了一种基于二级矢量优化的简化模型预测电流控制算法,在实现电机定子基波电流有效跟踪控制的同时有效抑制了定子电流的谐波及零序分量。文中基于矢量空间解耦理论对六相全桥逆变器的输出电压矢量进行了分层分析,以定子基波电流控制、谐波及零序电流抑制为准则对逆变器输出的729个电压矢量进行二级优化,得到候选的12个电压矢量,以此为基础设计了模型预测电流控制算法。实验结果表明,该简化模型预测电流控制方法具有良好的动静态性能,能在基波电流控制的同时有效抑制谐波及零序电流分量,可为多相电机驱动系统研究提供一定的理论支撑。

永磁同步电机直接转矩控制策略优化

针对传统直接转矩控制系统中的电磁转矩脉动问题,提出一种基于改进模型预测的永磁同步电机直接转矩控制策略。利用模型预测原理与直接转矩控制系统相结合的方法降低电机运行中的转矩脉动,设计了一种12扇区直接转矩控制方法优化模型预测,引入三段滞环控制器降低转矩脉动,并给出一种较为理想的备选电压矢量集合。采用MATLAB/Simulink仿真,并与优化电压矢量选择表后的模型预测控制、传统模型预测直接转矩控制进行对比。结果表明,所提方法使永磁同步电机在运行过程中保持良好动态响应能力的同时,有效降低了系统转矩脉动,使系统更加平稳。

Improved three-vector based dead-beat model predictive direct power control strategy for grid-connected inverters

Since only one inverter voltage vector is applied during each duty cycle, traditional model predictive direct power control(MPDPC) for grid-connected inverters(GCIs) results in serious harmonics in current and power. Moreover, a high sampling frequency is needed to ensure satisfactory steady-state performance, which is contradictory to its long execution time due to the iterative prediction calculations. To solve these problems, a novel dead-beat MPDPC strategy is proposed, using two active inverter voltage vectors and one zero inverter voltage vector during each duty cycle. Adoption of three inverter vectors ensures a constant switching frequency. Thus, smooth steady-state performance of both current and power can be obtained. Unlike the traditional three-vector based MPDPC strategy, the proposed three vectors are selected based on the power errors rather than the sector where the grid voltage vector is located, which ensures that the duration times of the selected vectors are positive all the time. Iterative calculations of the cost function in traditional predictive control are also removed, which makes the proposed strategy easy to implement on digital signal processors(DSPs) for industrial applications. Results of experiments based on a 1 kW inverter setup validate the feasibility of the proposed three-vector based dead-beat MPDPC strategy.

LCL型逆变器的积分IDA-PBC控制策略

本文基于LCL型逆变器采用互联和阻尼分配无源控制设计控制器,针对控制模型多变量相互耦合和控制结构复杂等问题,对互联和阻尼分配无源控制(IDA-PBC)模型进行等效处理,建立IDA-PBC的去耦等效控制模型,基于该模型提出了一种注入阻尼参数设计方法,推导计算注入阻尼的大小和范围;为了减小并网电流的稳态误差,在IDA-PBC的基础上引入积分控制器,并提出了一种积分IDA-PBC控制策略,动态调节时采用注入阻尼,稳态时采用积分控制,该控制策略兼顾了系统动静态性能,提高系统的全局稳定性。最后,经过实验证明了提出的参数设计方法的合理性以及改进控制策略的可行性。