Space vector-based analysis of overmodulation in triangle-comparison based PWM for voltage source inverter

The equivalence of triangle-comparison-based pulse width modulation (TCPWM) and space vector based PWM (SVPWM) during linear modulation is well-known. This paper analyses triangle-comparison based PWM techniques (TCPWM) such as sine-triangle PWM (SPWM) and common-mode voltage injection PWM during overmodulation from a space vector point of view. The average voltage vector produced by TCPWM during overmodulation is studied in the stationary (a–b) reference frame. This is compared and contrasted with the average voltage vector corresponding to the well-known standard two-zone algorithm for space vector modulated inverters. It is shown that the two-zone overmodulation algorithm itself can be derived from the variation of average voltage vector with TCPWM. The average voltage vector is further studied in a synchronously revolving (d-q) reference frame. The RMS value of low-order voltage ripple can be estimated, and can be used to compare harmonic distortion due to different PWM methods during overmodulation. The measured values of the total harmonic distortion (THD) in the line currents are presented at various fundamental frequencies. The relative values of measured current THD pertaining to different PWM methods tally with those of analytically evaluated RMS voltage ripple.     

Generalised direct positioning approach for multilevel space vector modulation: theory and DSP?implementation

In three-phase DC-AC multilevel converters, the space vector modulation is the preferred pulse width modulation (PWM) technique. A particular area relative to the space vector modulation (SVM) analysis for multilevel converter is focused and a direct positioning approach for finding the location of the reference vector among available triangles within the SVM diagram is proposed. The developed procedure is then generalised for an n-level converter by proposing a (n - 1)² times 1 complex matrix that locates the exact place at the end of the reference vector. To verify the proposed method, the whole modulation process was implemented with DSP for three- and four-level converters. To prove the effectiveness of the proposed method in higher-level cases, it was also applied to five- and six-level SVMs. Experimental results validate the direct positioning approach to be an accurate and reliable technique for digital implementation purposes, reducing the total modulation time as well as saving it for complex control techniques needed in industrial applications of SVM.     

A novel sensorless control method for brushless DC motor

The authors present the theory and implementation of a novel sensorless control method for the interior permanent magnet (IPM) brushless DC motor (BLDCM). The proposed new sensorless technique can accurately detect the zero-cross point (ZCP) of back electromotive force (BEMF), which is based on a comparison of the terminal voltage of the un conducting phase during the first and second part of a pulse width modulation (PWM) cycle. Compared with the conventional BEMF sensorless approach, the proposed new sensorless method solves the problem of the sensorless BLDCM drives at very low speeds. Experimental results confirm the validity of the new method.     

Pulse width modulation technique with harmonic injection and frequency modulated carrier: formulation and application to an induction motor

A new generated pulse width modulation (PWM) technique is presented, making it possible to significantly reduce harmonics in comparison to currently used PWMs operating in real time. This improvement means that a motor connected to an inverter that is controlled with this technique undergoes less overheating and vibrations, thereby improving its performance.     

永磁同步电机无传感器控制仿真研究

介绍了高频信号注入法在永磁同步电机无传感器控制系统中的实现,采用矢量控制策略和电压空间矢量脉宽调制技术,构建了永磁同步电机无传感器控制系统的电流、转速双闭环控制模型,基于外差法设计了转子位置观测器,完成了对电机转子信息的获取,并在MATLAB/Simulink环境下进行了系统的仿真分析.仿真结果证明,该方法能够准确估计转子信息,且能满足矢量控制的要求.     

基于模型预测的三电平PWM变流器直接功率控制

为了满足脉宽调制型变流器功率响应速度快以及绝缘栅双极型晶体管开关频率恒定等要求,提出了基于模型预测的直接功率控制策略用于三电平PWM变流器。该控制策略采用电压外环、功率内环的双闭环控制,外环省略了锁相环环节,简化了控制系统结构;内环无需PI调节器,参数设计简单,响应速度快。利用MATLAB/SIMULINK仿真平台搭建了三电平中性点箝位型PWM变流器模型,对比分析了提出的控制策略与传统PI控制的效果。仿真结果表明,新的控制策略有效降低了交流侧电流总谐波失真率,提高了交流侧功率因数,具有良好的动态和稳态性能。     

A simple practical analytic design method for multiloop‐controlled PWM switching regulators

Abstract

In this paper, a simple practical analytic method is proposed for designing multiloop‐controlled pulse width modulation (PWM) switching regulators. First, an equivalent single loop gain is presented and an approximate optimal set of closed‐loop poles is suggested according to the given specification such that the familiar design concept of a single‐loop second order system can be applied directly. In particular, closed form expressions of the feedback gains and the unknown parameters of the standard implemented circuit are derived. This renders the implementation problem surprisingly simple. Finally, some experimental results are also presented to demonstrate the effectiveness of the proposed method.     

感应电机矢量控制系统仿真研究

针对基于空间矢量脉宽调制技术（SVPWM）和转子磁场定向控制原理的感应电机矢量控制系统,利用控制功能模块化的设计思想,在Matlab／Simulink中建立功能独立的子模块如矢量控制模块、速度控制模块、坐标变换模块、SVPWM子模块等,并将这些功能模块拼装组合,构建了电流、转速双闭环感应电机矢量控制仿真模型。仿真结果表明基于模块化设计的感应电机矢量控制仿真模型是有效可行的,为电机控制器的设计提供了一种途径。     

PWM optimisation for three-level voltage inverter based on clonal selection algorithm

A clonal selection algorithm (CSA) is first applied to determine the switching time for a three-level voltage pulse width modulation (PWM) inverter. To obtain an optimal PWM switching pattern, CSA should calculate a set of nonlinear transcendental equations with nonlinear equality and inequality constraints. Unlike the general CSA by penalising infeasible solutions, this new CSA deals with constraints and guides the search to the true optimum solution by an infeasibility degree with a random disturbance (IFDD) selection operation. The proposed method minimise the total harmonic distortion and generates a waveform with adjustable amplitude of the fundamental component. Calculation results verify that the proposed method is efficient to obtain the optimal PWM switching pattern and is superior to natural sampling and genetic algorithm-based PWM switching pattern.     

激光水下PPM通信中的脉宽稳定技术研究

云层使PPM光脉冲产生时间扩展。全信号检测带来困难。给出平均多路经时间扩展的计算式。并提出了克服困难的一种方法：将电脉冲非线性展宽，以减小云层厚度对脉宽度的影响。模拟实验表明，当输入脉冲宽度变化范围20ns-5μs时，输出脉冲宽度变化为1-5μs。     

Digital-to-analog conversion by pulse-count modulation methods

Three low-cost digital-to-analog converters (DACs) are described and compared. These designs can easily be implemented in an integrated circuit: the conventional pulse-width modulation (PWM) DAC, the new pulse-count modulation (PCM) DAC and the first-order noise shaping (FONS) DAC. All three methods control the ratio of the sum of all pulse durations to the constant total period. As the pulse durations are integral multiples of a unit pulse, all three can be classified as pulse-count modulation methods. Block diagrams of all three DACs consisting of a simple digital circuit and a low-pass filter are presented. For a constant digital input value the worst case ripple of the filter output is used to calculate the cutoff frequency of the low-pass filter. Approximations for the 3 dB cutoff frequency of first-order, second-order and fourth-order Butterworth low-pass filters are given. The dynamic properties are analyzed in the time domain (settling time) and in the frequency domain (unfiltered output spectrum of a full-scale sine wave input). The main influences on the static accuracy are analyzed. A case study demonstrates the abilities of PCM and FONS     

水声脉冲信号检测的新方法

水声脉冲信号是由一个运动平台上的发射器发射的。信号的调制方式、载频、幅度、脉宽以及周期均为未知。该文介绍了一种水声脉冲信号检测的新方法。水声脉冲信号接收机输出的短时谱重心是不断起伏的。起伏在高信噪比时会变得很小,而在低信噪比(或无信号)时会变得很大。由于,起伏的绝对偏差移动平均可用来度量起伏的大小,因此,它可以被用来检测水声脉冲信号。还介绍了新检测方法的原理、算法以及仿真结果。在海洋噪声、运动载体的辐射噪声以及小的多途干扰背景中,该方法能可靠地检测水声脉冲信号,并能同时对信号的一些参数作出估计。     

75kW超声波发生器控制信号研究

75kW超声波发生器的控制信号必须满足死区时间稳定,频率可调、稳定,能够间隙激发等要求。采用的是电压驱动型脉宽调制控制芯片TL494CN,其产生方波频率在15~40kHz范围内连续可调,死区时间为3μs。用NE555P产生调制波,该调制波信号与TL494CN产生的频率可调脉冲信号经调制后形成有间隙的方波信号,用于控制功率器件IGBT的驱动电路。从示波器记录的输出波形上可以看出:TL494CN生成的频率可调方波与NE555P产生的调制波经过调制电路后,得到能够间隙发射的控制信号。通过现场试验,该控制信号能够控制IGBT的驱动电路实现大功率超声的激发,且满足大功率超声激发的要求。     

Control of a converter system for an asymmetrical parameter type two-phase induction motor drive operating in motoring and generating modes

The control of a converter system is presented and discussed for an asymmetrical parameter type two-phase induction machine drive that is operating in motoring and generating modes. The proposed system consists of back-to-back voltage source converters. For a machine side, a three-leg voltage source converter provides both unbalanced and balanced two-phase output voltages with a scalar V/F control based on a carrier space vector pulse width modulation (SVPWM) technique. For a front end, a single-phase AC/DC doubled voltage converter with hysteresis current control is used to keep DC-link voltage constant, thus resulting in a bi-directional power flow operation for the motoring and generating modes. A closed-loop design for the DC-link voltage is fully given and also included is a review of carrier-based SVPWM for two-phase three-leg VSI. The proposed drive system was both simulated using MATLAB/SIMULINK and implemented on digital microcontrollers. The comparative performance evaluation of the whole system between balanced and unbalanced two-phase voltages for the machine is given. The simulation and experimental results show that the unbalanced phase voltage offers better performance for the whole system.     

Chirp signal matching and signal power optimization in pulse-echomode ultrasonic nondestructive testing

Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms should be applied which make full use of the available power and bandwidth resources. We report here two methods to improve the overall efficiency of an ultrasonic pulse-echo system. Transmitter signals with constant amplitude level and nonlinear frequency modulation can be generated in such a way that they are spectrally matched to the system. A formula for the calculation of such a matched nonlinear chirp signal is presented. This modulation scheme also leads to a side-lobe level reduction of the compressed pulses. The application of square wave chirps derived from sine type chirps yields an additional gain of echo signal amplitude. Moreover, the complexity of the signal generation hardware is reduced. The methods are illustrated by an example     

Optimality properties and performance analysis of co-operative time-reversal communication in wireless sensor networks

The properties and performance of a technique, called time reversal, for co-operative communication on power-constrained wireless sensor networks are studied. A brief discussion of the optimality properties of this approach is presented, and performance is studied experimentally via a simulated indoor environment containing multiple wireless sensors. Using numerical simulation, the behaviour of the peak power received at a target sensor as a function of the number of co-operating transmitting sensors as well as the level of transmitted signal distortion and timing synchronisation errors, is studied. The simulation results demonstrate that, subject to some rather stringent synchronisation requirements, time reversal is an effective generalisation of beamforming that provides an efficient basis for co-operative communication on broadband multipath channels     

Device‐Level Photonic Memories and Logic Applications Using Phase‐Change Materials

Inspired by the great success of fiber optics in ultrafast data transmission, photonic computing is being extensively studied as an alternative to replace or hybridize electronic computers, which are reaching speed and bandwidth limitations. Mimicking and implementing basic computing elements on photonic devices is a first and essential step toward all‐optical computers. Here, an optical pulse‐width modulation (PWM) switching of phase‐change materials on an integrated waveguide is developed, which allows practical implementation of photonic memories and logic devices. It is established that PWM with low peak power is very effective for recrystallization of phase‐change materials, in terms of both energy efficiency and process control. Using this understanding, multilevel photonic memories with complete random accessibility are then implemented. Finally, programmable optical logic devices are demonstrated conceptually and experimentally, with logic “OR” and “NAND” achieved on just a single integrated photonic phase‐change cell. This study provides a practical and elegant technique to optically program photonic phase‐change devices for computing applications.     

基于状态空间的PWM逆变器数字PI双环控制技术研究

主要研究了数字控制的实际应用情况以及脉宽调制(PWM)正弦波逆变器的特点,包括电流内环电压外环的双闭环控制。在建立逆变器控制系统状态空间模型的基础上,详细分析了外环为输出电压,内环为电感电流加负载电流前馈控制对应的控制策略的稳定性和动态响应。先对控制系统直接离散化,再利用极点配置的方法进行系统参数设计。从响应速度、外特性、稳定性方面进行了具体分析,结果说明在离散域里双环控制逆变器具有较好的动态响应速度和输出外特性。最后通过实验验证和仿真波形分析,证明这种双环控制技术能满足各项性能指标要求。     

Time and phase synchronisation via direct-path signal for bistatic synthetic aperture radar systems

Bistatic synthetic aperture radar (BiSAR) operates with distinct transmitter and receiver that are mounted on separate platforms. Such a spatial separation results in problems and special requirements that are either not encountered or encountered in less serious form for monostatic SAR. Directly associated with these requirements one has to solve the problems of highly accurate time and phase synchronisations. The impact of oscillator frequency instability on BiSAR is analysed, and a time and phase synchronisation technique via direct-path signal is proposed. With the proposed technique, the direct-path signal of transmitter is received with one appropriative antenna and divided into two channels, one is passed through an envelope detector and used to synchronise the sampling clock, and the other is down-converted and used to compensate the phase synchronisation errors. Finally, the residual time synchronisation error is compensated with range alignment, and the residual phase synchronisation error is compensated with global positioning system/inertial navigation system/inertial measurement units (GPS/INS/IMU) information; then the focusing of BiSAR image can be achieved. Based on this technique, a prototype linearly frequency modulated BiSAR synchronisation system is constructed.The effectiveness of this proposed technique is verified with simulation data.