A neural-network-based space-vector PWM controller for voltage-fed inverter induction motor drive

A neural-network-based implementation of space-vector modulation (SVM) of a voltage-fed inverter has been proposed in this paper that fully covers the undermodulation and overmodulation regions linearly extending operation smoothly up to square wave. A neural network has the advantage of very fast implementation of an SVM algorithm that can increase the converter switching frequency, particularly when a dedicated application-specific integrated circuit chip is used in the modulator. The scheme has been fully implemented and extensively evaluated in a V/Hz-controlled 5 hp, 60 Hz, 230 V induction motor drive. The performances of the drive with artificial-neural-network-based SVM are excellent. The scheme can be easily extended to a vector-controlled drive.     

A stator-flux-oriented vector-controlled induction motor drive withspace-vector PWM and flux-vector synthesis by neural networks

A stator-flux-oriented vector-controlled induction motor drive is described where the space-vector pulsewidth modulation (SVM) and stator-flux-vector estimation are implemented by artificial neural networks (ANNs). ANNs, when implemented by dedicated hardware application-specific integrated circuit chips, provide extreme simplification and fast execution for control and feedback signal processing functions in high-performance AC drives. In the proposed project, a feedforward ANN-based SVM, operating at 20 kHz sampling frequency, generates symmetrical pulsewidth modulation (PWM) pulses in both undermodulation and overmodulation regions covering the range from DC (zero frequency) up to square-wave mode at 60 Hz. In addition, a programmable cascaded low-pass filter (PCLPF), that permits DC offset-free stator-flux-vector synthesis at very low frequency using the voltage model, has been implemented by a hybrid neural network which consists of a recurrent neural network (RNN) and a feedforward neural network (FFANN). The RNN-FFANN-based flux estimation is simple, permits faster implementation, and gives superior transient performance when compared with a standard digital-signal-processor-based PCLPF. A 5 HP open-loop volts/Hz-controlled drive incorporating the proposed ANN-based SVM and RNN-FFANN-based flux estimator was initially evaluated in the frequency range of 1.0-58 Hz to validate the performance of SVM and the flux estimator. Next, the complete 5 HP drive with stator-flux-oriented vector control was evaluated extensively using the PWM modulator and flux estimator     

Comparison of adaptive Neuro-Fuzzy-based space-vector modulation for two-level inverter

Space Vector Modulation (SVM) is an optimal pulse width modulation technique for an inverter used in variable frequency drive applications. This paper proposes a Neuro-Fuzzy based Space Vector Modulation (SVM) technique for voltage source inverter and its performance is compared with the conventional based SVM and Neural Network based SVM methods. This scheme is five-layer network, receives the d-axis and q-axis voltages information at the input side and generates the duty ratios as an output for the inverter circuit. The training data for Neural Network and adaptive Neuro-Fuzzy is generated by simulating the conventional SVM. Neuro-Fuzzy uses the hybrid learning algorithm for training the network. Due to this learning algorithm, the required training error can be obtained with less number of iterations compared to Neural Network. The simulation results obtained are verified experimentally using a DSPACE kit (DS1104). The simulation and experimental waveforms of inverter line–line voltages at different switching frequencies is presented. The Total Harmonic Distortion (THD) of line–line voltage with Neuro-Fuzzy, Neural Network and conventional based SVM methods for various switching frequencies are presented.     

A variable band universal flux/charge modulator for VSI and CSImodulation

This paper presents an integrated approach for closed-loop control of the output voltage of a voltage-source inverter and the output current of a current-source inverter, using hysteresis with a rectangular bounding box in the synchronous d-q reference frame and a simple set of switching rules. The modulator is constrained to only select from the two nearest active space vectors to the target reference, and hence achieves a significantly improved harmonic performance compared to Sigma-Delta and other stationary frame hysteresis modulators. A further refinement then adjusts the dimensions of the bounding box to restrict the switching process to two active space vectors (and null vectors) only within a constant switching period. This achieves a harmonic performance similar to open-loop space-vector modulation. Discontinuous modulation can also be implemented using an alternative dimension-varying strategy and, since the modulator is a closed-loop system, it exhibits excellent robustness to parameter variations and other system disturbances. The practicability and performance of the modulator under various modulation conditions have been verified both in simulation and experimentally     

Direct torque control of induction machines using space vectormodulation

A direct induction machine torque control method based on predictive, deadbeat control of the torque and flux is presented. By estimating the synchronous speed and the voltage behind the transient reactance, the change in torque and flux over the switching period is calculated. The stator voltage required to cause the torque and flux to be equal to their respective reference values is calculated. Space vector PWM is used to define the inverter switching state. An alternative approach to deadbeat control for use in the transient or pulse-dropping mode is also presented. An alternative modulation scheme is presented in which transient performance is improved by specifying the inverter switching states and then calculating the required switched instants to maintain deadbeat control of the flux while reducing the torque error during the entire switching interval. A similar approach is used for a transient in the flux. The implementation of the control scheme using DSP-based hardware is described, with complete experimental results given     

一种通用的H桥级联多电平逆变器SVPWM控制

H桥级联多电平逆变器调速系统中,电压矢量数目过多,存在计算困难及电压矢量优化选择的问题.对多电平系统电压矢量的特点和规律进行深入分析,提出了一种简单、通用的电压空间矢量脉宽调制( SVPWM)控制算法.该算法可减小谐波畸变,降低开关频率,能很容易地确定参考电压矢量位置和各矢量作用时间,且占用存储空间小,无需查表.最后,通过13电平H桥级联型逆变器驱动系统的实验,验证了该方法的有效性.     

零序分量注入型三电平感应电动机矢量控制系统

提出一种基于三电平中点箝位(NPC)逆变器的零序分量注入型感应电动机矢量控制方案。系统中使用快速电流控制的直接转子磁链定向矢量控制模式,由于定子电流是由快速电流环控制,因此系统中不用使用定子电压方程,并且不需要解耦电路。转子磁链位置角由磁通模型计算得到。感应电动机由三电平NPC逆变器供电,三电平NPC逆变器由于开关器件的电压应力是传统两电平逆变器开关器件上电压应力的一半,所以适合用于中压调速系统。逆变器控制采用开关优化PWM算法,通过注入零序分量,不但优化功率器件的开关频率,而且可以稳定中点电位。仿真结果表明,该方法在三电平逆变器供电的感应电动机上有效地实现了矢量控制,并且具有很好的性能。     

变频器的电压空间矢量调制控制技术研究

和SPWM控制相比,空间矢量调制(SVM)技术对直流母线电压的利用率高,适合数字实现.本研究项目是为铁道客车空调机组供电的电压SVM控制变频电源,变频器采用开环起动和稳态电压闭环控制,讨论了恒定V/F控制和电压闭环调节的实现原理,在查表法的基础上提出"复用空间矢量法".该方法可以提高开关频率,降低低频输出电压的失真度并节省存储空间.通过系统辨识建立了电压空间矢量调制变频器的模型,设计了数字电压调节器.仿真和40kVA原理样机的实验测试结果证明所提控制方案可行.     

中点箝位型三电平逆变器空间矢量与虚拟空间矢量的混合调制方法

中点电压偏移是中点箝位型(neutral point clamped,NPC)多电平逆变器的主要缺点。空间矢量脉宽调制(space vector pulse-width modulation,SVPWM)由于算法本身的缺陷,在调制度较高且功率因数较低时,电容电压出现低频波动。虚拟空间矢量调制(virtual SVPWM, VSVPWM)方法能够在全范围内处理中点电压偏移问题,但存在开关次数较多,谐波特性较差的缺点。该文建立含电容电压的NPC三电平逆变器的PWM模型,讨论SVPWM和VSVPWM的约束条件。在特定的区域采用SVPWM,其他区域采用VSVPWM,给出了这2种调制策略的切换条件。实验结果表明,混合调制方法(hybrid PWM,HPWM)较之以前的解决方案能够更好的平衡电容电压,并且也能够有效的降低开关次数和提高逆变器输出的谐波特性。     

Three-level Inverter-fed Induction Motor Drive Performance Improvement with Neuro-fuzzy Space Vector Modulation

—The space vector modulation technique is an optimal pulse-width modulation technique used for inverter control. This article presents a neuro-fuzzy-based space vector modulation technique for a three-level inverter fed induction motor. It uses a hybrid learning algorithm (combination of back-propagation and least-squares methods) for training the input–output data pattern. The training data for neuro-fuzzy-based space vector modulation are generated from the conventional simplified space vector modulation method. The proposed scheme uses the space vector rotation angle and change of rotation angle information as input and generated duty ratios as output. The dynamic and steady-state performance of a neuro-fuzzy-controlled induction motor drive is compared with the conventional space vector modulation and neural network-based space vector modulation methods. The simulation results obtained are verified experimentally using a dSPACE kit (DS1104). The performance measure in terms of the total harmonic distortion of inverter line–line voltage of the neuro-fuzzy-based system is compared with the neural network-based space vector modulation and conventional space vector modulation methods.     

A 7.5 kW ultrasonic inverter motor drive employing MOS-controlledthyristors

The design and performance of an inverter induction motor drive that employs an ultrasonic switching frequency to minimize audible noise is described. The MOS-controlled thyristor (MCT) is a high-speed power semiconductor with the potential for high voltage and current ratings. Distinctive features of the device are discussed relative to inverter topology, gate drive requirements, and fault protection. Since MCT devices of sufficient rating were not available, insulated-gate-bipolar-transistor (GBT) devices were used in the experimental model. MCT and IGBT devices have comparable switching times. The design of a 7.5 kW and 20 kHz inverter is discussed, including a modified pulsewidth modulation (PWM) switching algorithm conducive to microprocessor implementation. The algorithm requires reduced computational and storage requirements over previous PWM methods. Implementation of the algorithm is accomplished by a digital signal processor using the efficient C language. Experimental waveforms are presented     

混合钳位式双PWM三电平变频调速系统

以电动机磁链定向调速系统为研究对象, 提出了一种混合钳位式双PWM三电平变换器的电路拓扑, 由于混合钳位式三电平变换器的开关状态由普通二极管钳位式的27个增加到64个, 本文提出了通过检测的悬浮电容电压和直流侧电容电压差值来实现冗余矢量的优化方法, 确保了直流电容电压的平衡, 实现了系统的四象限运行.并设计了基于DSP和CPLD的控制电路和主电路,通过实验验证了所提算法的有效性和实用性.     

中点电压偏移对SVM控制的三电平逆变器的影响及补偿措施

简要介绍了三电平逆变器的传统SVM控制算法.针对逆变器负载运行时,负载动态特性对于三电平逆变器的中点电压的影响,以及由中点电压偏移造成的空间矢量图的变化,引入中点电压前馈控制方法,进行新的矢量分区和作用时间计算,从而改进逆变器带负载时的输出电流波形.在Matlab软件平台上进行仿真,结果表明改进的SVM得到的输出电流波形较传统的SVM控制方法下的输出电流波形有明显的改善.     

动车组三相三电平T型逆变拓扑及其简化调制

针对传统动车组NPC三电平逆变器拓扑结构和调制算法的复杂性,对T型拓扑进行分析,阐述了T型拓扑的特点和能平衡器件损耗的优点。进一步简化了三电平逆变的SVPWM调制方法,同时对中点电压不平衡引入调节系数进行控制。最后进行了仿真验证。结果表明,T型结构引入中点电位调节系数后具有较好的带不平衡负载的能力,证实了T型结构的正确性与在动车组牵引传动中应用的有效性。     

一种简单的异步电动机直接转矩控制方法研究

在基于开关表的直接转矩控制(ST-DTC)方法的基础上,通过PI调节得到补偿定子磁链和转矩误差的参考电压矢量,利用空间电压矢量调制(SVM)技术将相应的参考电压矢量转化为逆变器开关信号以实现对异步电机的控制。在Matlab/Simulink中建模仿真后发现,这一方法能固定逆变器开关频率并降低转矩和电流脉动,低速性能也较传统DTC方法更为优越,控制简单有效。     

A Simple Space Vector PWM Scheme to Operate a Three-Level NPC Inverter at High Modulation Index Including Overmodulation Region, With Neutral Point Balancing

Three-level neutral point clamped (NPC) inverter is a widely used topology of multilevel inverters. However, the neutral point fluctuates for certain switching states. At low modulation index, the fluctuations can be compensated using redundant switching states. But, at higher modulation index and in overmodulation region, the neutral point fluctuation deteriorates the performance of the inverter. This paper proposes a simple space vector pulsewidth modulation scheme for operating a three-level NPC inverter at higher modulation indexes, including overmodulation region, with neutral point balancing. Experimental results are provided     

Space vector PWM for a two-phase VSI

This paper proposes space vector pulse width modulation (SVPWM) technique to control a two-phase full bridge voltage source inverter (VSI) having reduced number of static switches with higher phase voltage output. SVPWM gives higher fundamental component amplitude, provides more efficient use of DC supply voltage and generates less harmonic distortion in the output voltages and currents than other pulse width modulation (PWM) techniques. Between asymmetric and symmetric SVPWM only symmetric one is considered so that the harmonic contents are minimized and two different timing sequences and corresponding switching states are proposed. For the implementation three level switching patterns are determined by using software. For real time application these theoretically determined switching signals for the six power transistors are generated by a digital signal processor (DSP) kit and finally the two-phase output voltages are applied to load. The experimental results are found good and in agreement with the theoretical results. Mathematical analysis along with theoretical and experimental performance of the proposed inverter are presented. Total harmonic distortion (THD) and distortion factor (DF) show that the output voltage quality is good enough to apply in any type of practical two-phase load.     

三电平逆变器开关管电压应力解决方案研究

三电平二极管钳位型桥式变流器是适应高电压、大功率应用环境比较好的方案。然而,三电平逆变器开关管在开通关断过程中普遍存在电压应力超标问题。为了解决上述问题,对三电平逆变器开关管应力进行分析后提出了开关管驱动保护电路,设计并优化了三电平的驱动波形。最后,在三电平逆变器实验平台上进行试验验证了该方法的有效性。     

T型三电平逆变器馈电双三相PMSM直接转矩控制

提出了一种T型三电平逆变器馈电双三相PMSM驱动系统直接转矩控制(DTC)策略。该系统既具有多相电机转矩脉动小、电流应力小和故障容错能力强的优点,也继承了T型三电平电机驱动谐波性能好、可靠性高的特点。该文所提出的基于双空间矢量调制(SVM)技术的直接转矩控制策略保留了DTC快速动态响应特性。与基于空间矢量解耦(VSD)的SVM技术相比,双SVM技术避免了复杂的矢量合成过程,并具有良好的谐波控制效果。所提出的控制策略还设计了谐波电流闭环控制器,能够有效抑制由绕组不对称、反电动势谐波、死区等非线性因素引起的低次谐波电流。通过实验验证了所提出的T型三电平逆变器馈电双三相PMSM驱动系统DTC策略的有效性。     

基于混合七电平电压型逆变器的新型6kV变频器

提出了一种基于混合七电平电压型逆变器的6kV变频器。混合七电平逆变器由1个采用10CT的三相中点箝位三电平逆变器和3个采用IGBT的H桥逆变器串联而成，可充分利用IGCT高压大容量及IGBT高速的特点。PWM控制采用基于参考电压分解的多电平直接PWM算法。数字化实现容易。采用了改进的死区效应补偿方法以获得理想的输出波形。研制了1台基于混合七电平逆变器的交流380V变频调速实验样机。实验结果为新型6kV变频器工业装置的研制打下了基础。